Method for accessing another plmn to deal with network failure

ABSTRACT

A disclosure of the present specification provides a method for accessing another Public Land Mobile Network (PLMN) instead of a subscribed third PLMN. According to the method, a terminal may access a second PLMN, which provides a service, instead of a first PLMN that is roaming-agreed with the third PLMN. In addition, according to the method, the terminal may display, on a screen, information indicating that access is made to the second PLMN. The second PLMN may provide only a limited service.

TECHNICAL FIELD

The present specification relates to mobile communication.

BACKGROUND

System Architecture Evolution (SAE) that has been performed based on 3rdGeneration Partnership Project (3GPP) Service and System Aspects (SA)Working Group 2 (WG2) is research regarding network technology that aimsto determine the structure of a network and to support mobility betweenheterogeneous networks in line with an LTE task of a 3GPP TechnicalSpecification Group (TSG) Radio Access Network (RAN) and is one ofrecent important standardization issues of 3GPP. SAE is a task fordeveloping a 3GPP system into a system that supports various radioaccess technologies based on an Internet Protocol (IP), and the task hasbeen carried out for the purpose of an optimized packet-based systemwhich minimizes transmission delay with a more improved datatransmission capability.

An Evolved Packet System (EPS) higher level reference model defined in3GPP SA WG2 includes a non-roaming case and roaming cases having variousscenarios, and for details therefor, reference can be made to 3GPPstandard documents TS 23.401 and TS 23.402. A network configuration ofFIG. 1 has been briefly reconfigured from the EPS higher level referencemodel.

FIG. 1 shows a structure of an evolved mobile communication network.

An Evolved Packet Core (EPC) may include various elements. FIG. 1illustrates a Serving Gateway (S-GW) 52, a Packet Data Network Gateway(PDN GW) 53, a Mobility Management Entity (MME) 51, a Serving GeneralPacket Radio Service (GPRS) Supporting Node (SGSN), and an enhancedPacket Data Gateway (ePDG) that correspond to some of the variouselements.

The S-GW 52 is an element that operates at a boundary point between aRadio Access Network (RAN) and a core network and has a function ofmaintaining a data path between an eNodeB 22 and the PDN GW 53.Furthermore, if a terminal (or User Equipment (UE)) moves in a region inwhich service is provided by the eNodeB 22, the S-GW 52 plays a role ofa local mobility anchor point. That is, for mobility within an E-UTRAN(Evolved Universal Mobile Telecommunications System (Evolved-UMTS)Terrestrial Radio Access Network defined after 3GPP release-8), packetscan be routed through the S-GW 52. Furthermore, the S-GW 52 may play arole of an anchor point for mobility with another 3GPP network (i.e., aRAN defined prior to 3GPP release-8, for example, a UTRAN or GlobalSystem for Mobile communication (GSM)/Enhanced Data rates for GlobalEvolution (EDGE) Radio Access Network (GERAN)).

The PDN GW (or P-GW) 53 corresponds to the termination point of a datainterface toward a packet data network. The PDN GW 53 can support policyenforcement features, packet filtering, charging support, etc.Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor pointfor mobility management with a 3GPP network and a non-3GPP network(e.g., an untrusted network, such as an Interworking Wireless Local AreaNetwork (I-WLAN), a trusted network, such as a Code Division MultipleAccess (CDMA)).

In the network configuration of FIG. 1, the S-GW 52 and the PDN GW 53have been illustrated as being separate gateways, but the two gatewaysmay be implemented in accordance with a single gateway configurationoption.

The MME 51 is an element for performing the access of a terminal to anetwork connection and signaling and control functions for supportingthe allocation, tracking, paging, roaming, handover, etc. of networkresources. The MME 51 controls control plane functions related tosubscribers and session management. The MME 51 manages numerous eNodeBs22 and performs conventional signaling for selecting a gateway forhandover to another 2G/3G networks. Furthermore, the MME 51 performsfunctions, such as security procedures, terminal-to-network sessionhandling, and idle terminal location management.

The SGSN handles all packet data, such as a user's mobility managementand authentication for different access 3GPP networks (e.g., a GPRSnetwork and an UTRAN/GERAN).

The ePDG plays a role of a security node for an unreliable non-3GPPnetwork (e.g., an I-WLAN and a Wi-Fi hotspot).

As described with reference to FIG. 1, a terminal (or UE) having an IPcapability can access an IP service network (e.g., IMS), provided by aservice provider (i.e., an operator), via various elements within an EPCbased on non-3GPP access as well as based on 3GPP access.

Furthermore, FIG. 1 shows various reference points (e.g., S1-U andS1-MME). In a 3GPP system, a conceptual link that connects two functionsthat are present in the different function entities of an E-UTRAN and anEPC is called a reference point. Table 1 below defines reference pointsshown in FIG. 1. In addition to the reference points shown in theexample of Table 1, various reference points may be present depending ona network configuration.

TABLE 1 REFERENCE POINT DESCRIPTION S1-MME A reference point for acontrol plane protocol between the E-UTRAN and the MME S1-U A referencepoint between the E-UTRAN and the S-GW for path switching betweeneNodeBs during handover and user plane tunneling per bearer S3 Areference point between the MME and the SGSN that provides the exchangeof pieces of user and bearer information for mobility between 3GPPaccess networks in idle and/or activation state. This reference pointcan be used intra-PLMN or inter-PLMN (e.g. in the case of Inter- PLMNHO). S4 A reference point between the SGW and the SGSN that providesrelated control and mobility support between the 3GPP anchor functionsof a GPRS core and the S-GW. Furthermore, if a direct tunnel is notestablished, the reference point provides user plane tunneling. S5 Areference point that provides user plane tunneling and tunnel managementbetween the S-GW and the PDN GW. The reference point is used for S-GWrelocation due to UE mobility and if the S-GW needs to connect to anon-collocated PDN GW for required PDN connectivity S11 A referencepoint between the MME and the S-GW SGi A reference point between the PDNGW and the PDN. The PDN may be a public or private PDN external to anoperator or may be an intra- operator PDN, e.g., for the providing ofIMS services. This reference point corresponds to Gi for 3GPP access.

Among the reference points shown in FIG. 1, S2a and S2b correspond tonon-3GPP interfaces. S2a is a reference point that provides relatedcontrol and mobility support between trusted non-3GPP access and PDN GWsto the user plane. S2b is a reference point that provides relatedcontrol and mobility support between ePDG and P-GW to the user plane.

FIG. 2 is an exemplary diagram showing the general functions of the mainnodes of the E-UTRAN and the EPC.

As shown, the eNodeB 20 may perform functions for routing to a gatewaywhile the RRC connection is active, scheduling and transmission ofpaging messages, scheduling and transmission of a Broadcast Channel(BCH), dynamic allocation of resources in uplink and downlink to the UE,configuration and provision for measurement of the eNodeB 20, radiobearer control, radio admission control, and connection mobilitycontrol, etc. Within the EPC, the eNodeB 20 may perform paginggeneration, LTE_IDLE state management, user plane encryption, EPS bearercontrol, encryption and integrity protection of NAS signaling.

FIG. 3 is an exemplary diagram showing the structure of a radiointerface protocol in the control plane between the UE and the eNodeB.FIG. 4 is another exemplary diagram showing the structure of a radiointerface protocol in the user plane between the UE and the eNB.

The radio interface protocol is based on the 3GPP radio access networkstandard. The radio interface protocol horizontally consists of aphysical layer, a data link layer, and a network layer. The radiointerface protocol is vertically divided into a user plane fortransmitting data information and a control plane for transmitting acontrol signal.

The protocol layers may be divided into L1 (Layer 1), L2 (Layer 2), andL3 (Layer 3) based on the lower three layers of the Open SystemInterconnection (OSI) standard model widely known in communicationsystems.

Hereinafter, each layer of the radio protocol in the control plane shownin FIG. 3 and the radio protocol in the user plane shown in FIG. 4 willbe described.

The first layer, the physical layer, provides an information transferservice using a physical channel The physical layer is connected to anupper Medium Access Control (MAC) layer through a transport channel, anddata between the MAC layer and the physical layer is transmitted throughthe transport channel And, data is transferred between differentphysical layers, that is, between the physical layers of thetransmitting side and the receiving side through a physical channel

A physical channel consists of several subframes on the time axis andseveral sub-carriers on the frequency axis. Here, one sub-frame iscomposed of a plurality of symbols on the time axis and a plurality ofsub-carriers. One subframe is composed of a plurality of resourceblocks, and one resource block is composed of a plurality of symbols anda plurality of subcarriers. A Transmission Time Interval (TTI), which isa unit time for data transmission, is 1 ms corresponding to onesubframe.

According to 3GPP LTE, the physical channels existing in the physicallayers of the transmitting side and the receiving side may be dividedinto a data channel, i.e., Physical Downlink Shared Channel (PDSCH) anda Physical Uplink Shared Channel (PUSCH), and a control channel, i.e., aPhysical Downlink Control Channel (PDCCH), a Physical Control FormatIndicator Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel(PHICH), and a Physical Uplink Control Channel (PUCCH).

The PCFICH transmitted in the first OFDM symbol of the subframe carriesa Control Format Indicator (CFI) regarding the number of OFDM symbolsused for transmission of control channels in the subframe (i.e., thesize of the control region). The wireless device first receives the CFIon the PCFICH and then monitors the PDCCH.

Unlike the PDCCH, the PCFICH does not use blind decoding and istransmitted through a fixed PCFICH resource of a subframe.

The PHICH carries a Positive-Acknowledgement(ACK)/Negative-Acknowledgement (NACK) signal for a UL Hybrid AutomaticRepeat Request (HARQ). An ACK/NACK signal for uplink (UL) data on aPUSCH transmitted by a wireless device is transmitted on a PHICH.

A Physical Broadcast Channel (PBCH) is transmitted in the first fourOFDM symbols of the second slot of the first subframe of the radioframe. The PBCH carries system information essential for a wirelessdevice to communicate with a base station, and the system informationtransmitted through the PBCH is called a Master Information Block (MIB).In comparison, the system information transmitted on the PDSCH indicatedby the PDCCH is referred to as a System Information Block (SIB).

PDCCH may carry resource allocation and transmission format of aDownlink Shared Channel (DL-SCH), resource allocation information of anUplink Shared Channel (UL-SCH), paging information on the PCH, systeminformation on the DL-SCH, resource allocation of a higher layer controlmessage such as a random access response transmitted on the PDSCH, a setof transmission power control commands for individual UEs in anarbitrary UE group, and activation of Voice over Internet Protocol(VoIP). A plurality of PDCCHs may be transmitted in the control region,and the UE may monitor the plurality of PDCCHs. The PDCCH is transmittedon an aggregation of one or several consecutive Control Channel Elements(CCEs). The CCE is a logical allocation unit used to provide the PDCCHwith a coding rate according to the state of a radio channel The CCEcorresponds to a plurality of resource element groups. The format of thePDCCH and the possible number of bits of the PDCCH are determinedaccording to the correlation between the number of CCEs and the codingrates provided by the CCEs.

Control information transmitted through the PDCCH is referred to asDownlink Control Information (DCI). DCI may include PDSCH resourceallocation (this may also be called a DL grant), PUSCH resourceallocation (this may also be called an UL grant), a set of transmitpower control commands for individual UEs in an arbitrary UE groupand/or activation of Voice over Internet Protocol (VoIP).

In the second layer, there are several layers. First, the MAC layerplays a role in mapping various logical channels to various transportchannels, and plays a role in logical channel multiplexing that mapsmultiple logical channels to one transport channel. The MAC layer isconnected to the Radio Link Control (RLC) layer, which is the upperlayer, by a logical channel Logical channels are largely divided into acontrol channel for transmitting control plane information and a trafficchannel for transmitting user plane information according to the type ofinformation to be transmitted.

The RLC layer of the second layer plays a role in diving andconcatenating the data received from the upper layer to adjust the datasize so that the lower layer is suitable for data transmission in theradio section. In addition, in order to ensure the various Quality ofService (QoS) required by each Radio Bearer (RB), three operation modes,i.e., Transparent Mode (TM), Un-acknowledged Mode (UM, no responsemode), and Acknowledged Mode (AM, response mode), are provided. Inparticular, AM RLC performs a retransmission function through anAutomatic Repeat and Request (ARQ) function for reliable datatransmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layerplays a role in header compression to reduce the size of the IP packetheader which is relatively large and contains unnecessary controlinformation in order to efficiently transmit IP packets such as IPv4 orIPv6 in a radio section with a small bandwidth. This serves to increasethe transmission efficiency of the radio section by transmitting onlynecessary information in the header part of the data. In addition, inthe LTE system, the PDCP layer also performs a security function, whichconsists of ciphering to prevent data interception by a third party andintegrity protection to prevent data manipulation by a third party.

The Radio Resource Control (RRC) layer located at the top of the thirdlayer is defined only in the control plane, and are responsible for thecontrol of logical channels, transport channels and physical channelsrelated to the configuration, reconfiguration, and release of the RB. Inthis case, the RB means a service provided by the second layer for datatransfer between the UE and the E-UTRAN.

If there is an RRC connection between the RRC of the UE and the RRClayer of the wireless network, the UE is in the RRC connected mode,otherwise it is in the RRC idle mode.

Hereinafter, an RRC state of the UE and an RRC connection method will bedescribed. The RRC state refers to whether or not the RRC of the UE islogically connected to the RRC of the E-UTRAN. If it is connected, it iscalled an RRC_CONNECTED state, and if it is not connected, it is calledan RRC_IDLE state. Since the UE in the RRC_CONNECTED state has an RRCconnection, the E-UTRAN can determine the existence of the UE on percell, and thus can effectively control the UE. On the other hand, theE-UTRAN cannot detect the existence of the UE in the RRC_IDLE state, andthe core network manages the UE per Tracking Area (TA), which is largerregional unit than the cell. That is, the UE in the RRC_IDLE state isonly checked whether the UE exists in a larger area than the cell, andin order to receive a normal mobile communication service such as voiceor data, the UE should transit to the RRC_CONNECTED state. Each TA isidentified through a Tracking Area Identity (TAI). The UE may configurethe TAI through a Tracking Area Code (TAC), which is informationbroadcast in a cell.

When the user turns on the UE for the first time, the UE first searchesfor an appropriate cell, then establishes an RRC connection in thecorresponding cell, and registers information on the UE in the corenetwork. After this, the UE stays in the RRC_IDLE state. The UE stayingin the RRC_IDLE state (re)selects a cell as needed, and looks at systeminformation or paging information. This is called camping on the cell.The UE, which stayed in the RRC_IDLE state, establishes an RRCconnection with the RRC of the E-UTRAN through an RRC connectionprocedure and then transits to the RRC_CONNECTED state only when it isnecessary to establish an RRC connection. There are several cases inwhich the UE in the RRC_IDLE state needs to establish an RRC connection,e.g., when uplink data transmission is required for reasons such as auser's call attempt, or when a paging message is received from E-UTRAN,for transmission of a response message to the paging message.

The Non-Access Stratum (NAS) layer located above the RRC layer performsfunctions such as session management and mobility management.

Hereinafter, the NAS layer shown in FIG. 3 will be described in detail.

Evolved Session Management (ESM) belonging to the NAS layer performsfunctions such as default bearer management and dedicated bearermanagement, and is responsible for controlling the UE to use the PacketSwitched (PS) service from the network. The default bearer resource hasthe characteristic that it is allocated from the network when it isconnected to a specific PDN for the first time. At this time, thenetwork allocates an IP address usable by the UE so that the UE can usethe data service, and also allocates QoS of the default bearer. LTEsupports two types: a bearer with a Guaranteed Bit Rate (GBR) QoScharacteristic that guarantees a specific bandwidth for datatransmission and reception, and a non-GBR-bearer with a best effort QoScharacteristic without a bandwidth guarantee. do. In the case of adefault bearer, a non-GBR-bearer is allocated. In the case of adedicated bearer, a bearer having QoS characteristics of GBR or non-GBRmay be allocated.

The bearer allocated to the UE by the network is called an EPS bearer,and when the EPS bearer is allocated, the network allocates one ID. Thisis called the EPS bearer ID. One EPS bearer has QoS characteristics ofMaximum Bit Rate (MBR) and Guaranteed Bit Rate (GBR) or AggregatedMaximum Bit Rate (AMBR).

FIG. 5a is a flowchart illustrating a random access procedure in 3GPPLTE.

The random access procedure is used for the UE 10 to obtain ULsynchronization with the base station, i.e., the eNodeB 20, or to beallocated UL radio resources.

The UE 10 receives a root index and a Physical Random Access Channel(PRACH) configuration index from the eNodeB 20. There are 64 candidaterandom access preambles defined by a Zadoff-Chu (ZC) sequence for eachcell, and the root index is a logical index for the UE to generate 64candidate random access preambles.

Transmission of the random access preamble is limited to specific timeand frequency resources for each cell. The PRACH configuration indexindicates a specific subframe and preamble format in which the randomaccess preamble can be transmitted.

The UE 10 transmits a randomly selected random access preamble to theeNodeB 20. The UE 10 selects one of 64 candidate random accesspreambles. Then, the UE 10 selects a corresponding subframe according tothe PRACH configuration index. The UE 10 transmits the selected randomaccess preamble in the selected subframe.

Upon receiving the random access preamble, the eNodeB 20 transmits aRandom Access Response (RAR) to the UE 10. The random access response isdetected in two steps. First, the UE 10 detects a PDCCH masked with aRandom Access Radio Network Temporary Identity (RA-RNTI). The UE 10receives a random access response in a MAC Protocol Data Unit (PDU) onthe PDSCH indicated by the detected PDCCH.

FIG. 5b shows a connection process in an RRC layer.

As shown in FIG. 5 b, the RRC state is indicated depending on whetherRRC is connected or not. The RRC state means whether or not the entityof the RRC layer of the UE 10 is in logical connection with the entityof the RRC layer of the eNodeB 20. A state that is connected is calledan RRC connected state, and a state that is not connected is called anRRC idle state.

Since the UE 10 in the connected state has an RRC connection, theE-UTRAN can determine the existence of the corresponding UE on per cell,and thus can effectively control the UE 10. On the other hand, the UE 10in the idle state cannot be detected by the eNodeB 20, and is managed bythe core network in a tracking area unit, which is a larger area unitthan the cell. The tracking area is an aggregate unit of cells. That is,only the existence of the UE 10 in the idle state is determined in alarge area unit, and in order to receive a normal mobile communicationservice such as voice or data, the UE should transit to the connectedstate.

When the user turns on the UE 10 for the first time, the UE 10 firstsearches for an appropriate cell and then stays in an idle state in thecorresponding cell. The UE 10, which stayed in the idle state,establishes an RRC connection with the RRC layer of the eNodeB 20through an RRC connection procedure and transits to an RRC connectedstate only when it needs to establish an RRC connection.

There are several cases in which the UE in the idle state needs toestablish an RRC connection, e.g., a user's call attempt or when uplinkdata transmission is required, or when a paging message is received fromthe E-UTRAN, for transmission of the response message.

In order for the UE 10 in the idle state to establish an RRC connectionwith the eNodeB 20, an RRC connection procedure should be performed asmentioned above. The RRC connection process includes, largely, a processin which the UE 10 transmits an RRC connection request message to theeNodeB 20, a process in which the eNodeB 20 transmits an RRC connectionsetup message to the UE 10, and a process in which the UE 10 transmitsan RRC connection setup complete message to the eNodeB 20. This processwill be described in more detail with reference to FIG. 5b as follows.

When the UE 10 in the idle state wants to establish an RRC connectionfor reasons such as a call attempt, a data transmission attempt, or aresponse to a paging of the eNodeB 20, first, the UE 10 transmits a RRCconnection request message to the eNodeB 20.

Upon receiving the RRC connection request message from the UE 10, theeNB 20 accepts the RRC connection request of the UE 10 if the radioresources are sufficient, and transmits a RRC connection setup messageas a response message to the UE 10.

Upon receiving the RRC connection setup message, the UE 10 transmits anRRC connection setup complete message to the eNodeB 20. When the UE 10successfully transmits the RRC connection establishment message, the UE10 establishes an RRC connection with the eNodeB 20 and transits to theRRC connected mode.

<Network Failure>

Meanwhile, a failure may occur in the base station of the first PublicLand Mobile Network (PLMN) by the first operator, and a situation mayoccur in which a mobile communication service cannot be provided anylonger through the corresponding base station.

A simple failure can be restored within a short period of time, but whena failure occurs due to fire, flooding, etc., it may not be restored forhours or days. In this case, simple communication may causeinconvenience to the user, but interruption of important communication(e.g., emergency call (119 or 911 call) or corporate Virtual PrivateNetwork (VPN) communication) may cause a major problem.

Therefore, when a failure occurs in the first PLMN by the firstoperator, another second operator should be able to provide services forsubscribers of the first operator on behalf of the first operator.

However, there is a problem that a technical method for this has notbeen proposed so far.

SUMMARY

Accordingly, an object of the present specification is to propose amethod for solving the above-described problems.

In order to achieve the above object, a disclosure of the presentspecification provides a method of accessing another Public Land MobileNetwork (PLMN) instead of a subscribed third PLMN. According to themethod, a User Equipment (UE) may access a second PLMN providing aservice on behalf of a first PLMN which has a roaming agreement with thethird PLMN. And according to the method, the UE may display informationindicating access to the second PLMN on a screen. The second PLMN mayprovide only a limited service.

In order to achieve the above object, a disclosure of the presentspecification may provide a User Equipment (UE) accessing another PublicLand Mobile Network (PLMN) instead of a subscribed third PLMN. The UEmay include a transceiver configured to access a second PLMN providing aservice on behalf of a first PLMN which has a roaming agreement with thethird PLMN. The UE may include a display unit configured to displayinformation indicating access to the second PLMN on a screen of the UE.The second PLMN may provide only a limited service.

According to the disclosure of the present specification, it is possibleto solve the problems of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of an evolved mobile communication network.

FIG. 2 is an exemplary diagram showing the general functions of the mainnodes of the E-UTRAN and the EPC.

FIG. 3 is an exemplary diagram showing the structure of a radiointerface protocol in the control plane between the UE and the eNodeB.

FIG. 4 is another exemplary diagram showing the structure of a radiointerface protocol in the user plane between the UE and the eNB.

FIG. 5a is a flowchart illustrating a random access procedure in 3GPPLTE.

FIG. 5b shows a connection process in an RRC layer.

FIG. 6 shows a connection between an EPC and an IP Multimedia Subsystem(IMS).

FIG. 7 is an exemplary diagram illustrating a roaming scheme of Voiceover LTE (VoLTE).

FIG. 8 is an exemplary signal flow diagram illustrating a process ofperforming IMS registration in a HR scheme in a situation in which theUE roams to a visited network.

FIG. 9 is a structural diagram of a next-generation mobile communicationnetwork.

FIG. 10 shows an example of an expected structure of next-generationmobile communication from a node perspective.

FIG. 11 shows an example of an architecture for supporting simultaneousaccess to two data networks.

FIG. 12 is another exemplary diagram showing the structure of a radiointerface protocol between the UE and the gNB.

FIG. 13 is a block diagram of a UE according to an embodiment.

FIG. 14 is a block diagram showing the configuration of a UE shown inFIG. 13 in more detail.

FIG. 15 is an exemplary diagram illustrating a screen of a UE accordingto an embodiment.

FIG. 16 is an exemplary diagram illustrating a screen of a UE accordingto an embodiment.

FIG. 17 is an exemplary diagram illustrating a screen of a UE.

FIG. 18 is an exemplary diagram illustrating applications of a UE.

FIG. 19 is an exemplary diagram illustrating a screen displayed by aphone application executed in a UE.

FIG. 20 is an exemplary diagram illustrating a setting screen of a UE.

FIG. 21 is a detailed block diagram of a processor of a UE forimplementing the examples shown in FIGS. 15 to 20.

FIG. 22a and FIG. 22b show an embodiment in which the disclosure of thepresent specification is applied to EPS.

FIG. 23a and FIG. 23b show an embodiment in which the disclosure of thepresent specification is applied to 5GS.

FIG. 24 illustrates a wireless communication system according to anembodiment.

FIG. 25 illustrates an example of 5G use scenarios.

FIG. 26 shows an AI system 1 according to an embodiment.

DETAILED DESCRIPTION

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentdisclosure. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the disclosure, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the specification includes themeaning of the plural number unless the meaning of the singular numberis definitely different from that of the plural number in the context.In the following description, the term “include” or “have” may representthe existence of a feature, a number, a step, an operation, a component,a part or the combination thereof described in the specification, andmay not exclude the existence or addition of another feature, anothernumber, another step, another operation, another component, another partor the combination thereof.

The terms “first” and “second” are used for the purpose of explanationabout various components, and the components are not limited to theterms “first” and “second”. The terms “first” and “second” are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present disclosure.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in greater detail with reference to the accompanying drawings.In describing the present disclosure, for ease of understanding, thesame reference numerals are used to denote the same componentsthroughout the drawings, and repetitive description on the samecomponents will be omitted. Detailed description on well-known artswhich are determined to make the gist of the disclosure unclear will beomitted. The accompanying drawings are provided to merely make thespirit of the disclosure readily understood, but not should be intendedto be limiting of the disclosure. It should be understood that thespirit of the disclosure may be expanded to its modifications,replacements or equivalents in addition to what is shown in thedrawings.

In the drawings, User Equipments (UEs) are shown for example. The UE mayalso be denoted a terminal or Mobile Equipment (ME), etc. The UE may bea portable device such as a laptop computer, a mobile phone, a PDA, asmartphone, a multimedia device, etc., or may be a stationary devicesuch as a PC or a car mounted device.

<Definition of Terms>

For a better understanding, the terms used herein are briefly definedbefore going to the detailed description of the disclosure withreference to the accompanying drawings.

GERAN: An abbreviation of GSM EDGE Radio Access Network, which refers toa radio access section connecting the core network of GSM/EDGE and theUE.

UTRAN: Abbreviation for Universal Terrestrial Radio Access Network,which refers to a radio access section connecting the core network of 3Gmobile communication and the UE.

E-UTRAN: An abbreviation of Evolved Universal Terrestrial Radio AccessNetwork, which refers to a radio access section connecting the corenetwork of the 4th generation mobile communication, i.e., LTE, and theUE.

UMTS: Abbreviation for Universal Mobile Telecommunication System, whichrefers to the core network of 3G mobile communication.

UE/MS: An abbreviation of User Equipment/Mobile Station, which refers toa terminal device.

EPS: An abbreviation of an Evolved Packet System, which refers to a corenetwork supporting a Long Term Evolution (LTE) network and to a networkevolved from an UMTS.

PDN: An abbreviation of a Public Data Network, which refers to anindependent network where a server for providing service is placed.

PDN connection: A connection from UE to a PDN, i.e., an association (orconnection) between UE represented by an IP address and a PDNrepresented by an APN.

PDN-GW (Packet Data Network Gateway): A network node of an EPS networkwhich performs functions of UE IP address allocation, packet screening &filtering, and charging data collection.

S-GW (Serving Gateway): A network node of an EPS network which performsfunctions of mobility anchor, packet routing, idle mode packetbuffering, and triggering an MME to page UE.

PCRF (Policy and Charging Rule Function): A node of an EPS network whichperforms policy decision to dynamically apply QoS and charging policiesdifferentiated for each service flow

APN (Access Point Name): A name of an access point that is managed in anetwork and provided to UE. That is, an APN is a character string thatdenotes or identifies a PDN. While requested service or a network (PDN)is accessed via P-GW, an APN is a name (a character string) previouslydefined within a network to search the so that the corresponding P-GWcan be searched for (e.g., ‘internet.mnc012.mcc345.gprs’).

TEID (Tunnel Endpoint Identifier): End point ID of the tunnelestablished between nodes in the network, and configured for eachsection per bearer of each UE.

NodeB: A base station of an UMTS network and is installed outdoors, ofwhich cell coverage corresponds to a macro cell.

eNodeB: A base station of an Evolved Packet System (EPS) and isinstalled outdoors, of which cell coverage corresponds to a macro cell.

(e)NodeB: A term referring to NodeB and eNodeB.

MME: An abbreviation of a Mobility Management Entity, and performsfunctions of controlling each entity within an EPS in order to provide asession and mobility for UE.

A session: A path for data transmission, and a unit thereof may be aPDN, a bearer, or an IP flow unit. The units may be classified into, asdefined in 3GPP, a unit of the entire target network (i.e., an APN orPDN unit), a unit classified based on QoS within the entire targetnetwork (i.e., a bearer unit), and a destination IP address unit.

PDN connection: A connection from UE to a PDN, i.e., an association (orconnection) between UE represented by an IP address and a PDNrepresented by an APN. It means a connection between entities (i.e.,UE-PDN GW) within a core network so that a session can be formed.

UE context: Information about the situation of UE which is used tomanage the UE in a network, i.e., situation information including an UEID, mobility (e.g., a current location), and the attributes of a session(e.g., QoS and priority, etc.)

NAS (Non-Access-Stratum): A higher stratum of a control plane between aUE and an MME. The NAS supports mobility management, session management,IP address management, etc., between the UE and the network.

RAT: An abbreviation of Radio Access Technology, which means GERAN,UTRAN, E-UTRAN, etc.

Meanwhile, the embodiments presented below may be implemented alone, butmay be implemented as a combination of several embodiments.

FIG. 6 shows a connection between an EPC and an IP Multimedia Subsystem(IMS).

Referring to FIG. 6, in the EPC, the MME 510, the S-GW 520, the P-GW 530a connected to the IMS, the P-GW 530 b connected to the Internet, thePolicy and Charging Rule Function (PCRF) 580 connected to the P-GW 530b, and the Traffic Detection Function (TDF) 590 connected to the PCRF580 are shown.

The TDF 590 detects the application and reports the detected applicationand description information about the service data flow of theapplication to the PCRF 580. The TDF 590 supports solicited applicationreporting and/or unsolicited application reporting.

IMS is a network technology that enables Packet Switching (PS) based onInternet Protocol (IP) to not only wired terminals but also wirelessterminals. It has been proposed to connect both wired terminals andwireless terminal via IP (i.e., All-IP).

The IMS-based network includes Call Session Control Function (CSCF) andInterconnection Border Control Functions (IBCF) 620 for handlingprocedures for control signaling, registration, and session. The CSCFmay include a Proxy-CSCF (P-CSCF) 610 and a Serving-CSCF (S-CSCF) 630.In addition, the CSCF may include an Interrogating-CSCF (I-CSCF). TheP-CSCF 610 operates as a first access point for UE in an IMS-basednetwork. Then, the S-CSCF 630 processes a session in the IMS network.That is, the S-SCSF 630 is an entity responsible for routing signaling,and routes a session in the IMS network. And, the I-CSCF operates as anaccess point with other entities in the IMS network.

Under the above IMS, an IP-based session is controlled by a SessionInitiation Protocol (SIP). The SIP is a protocol for controlling asession, and is a signaling protocol that specifies a procedure for UEswanting to communicate to identify each other and find their location,create a multimedia service session between them, or delete and changethe created session. The SIP uses a SIP Uniform Resource Identifier(URI) similar to an e-mail address to distinguish each user, so that aservice can be provided without being dependent on an IP address. TheseSIP messages are control messages, but are transmitted between the UEand the IMS network through the EPC user plane.

Referring to FIG. 6, the first P-GW 530 a of the EPC is connected to theP-CSCF 610 of the IMS, the P-CSCF 610 is connected to the IBCF 620, andthe IBCF 620 is connected to the S-CSCF 630.

In addition, the second P-GW 530 b of the EPC is connected to thenetwork of the Internet service provider.

FIG. 7 is an exemplary diagram illustrating a roaming scheme of Voiceover LTE (VoLTE).

As can be seen with reference to FIG. 7, in VoLTE roaming methods, thereare a Home Routed (HR) scheme and a Local Breakout (LBO) scheme.

According to the LBO scheme, the IMS signaling transmitted from the UEgoes through the S-GW/P-GW/P-CSCF in the Visited Public Land MobileNetwork (V-PLMN), and is forwarded to the S-CSCF in the Home PLMN(H-PLMN).

In the HR scheme, the IMS signaling transmitted from the UE goes throughthe S-GW in the V-PLMN, the P-GW/P-CSCF in the H-PLMN, and thenforwarded to the S-CSCF.

FIG. 8 is an exemplary signal flow diagram illustrating a process ofperforming IMS registration in a HR scheme in a situation in which theUE roams to a visited network.

As can be seen with reference to FIG. 8, the UE 100 is in a roamingstate in the visited network.

First, the UE 100 located in the visited network generates an IMS PDNwith a P-GW in the home network through the S-GW 520 b in the visitednetwork. Here, the IMS PDN may be a PDN for an IMS service, a PDN of awell-known IMS APN, or a PDN for a Voice over LTE service.

1) Next, when the UE 100 transmits a SIP-based REGISTER message to theS-GW 520 b in the visited network to perform IMS registration, the S-GW520 b in the visited network forwards the message to the P-CSCF 610 a inthe home network.

2) The P-CSCF 610 a forwards the message to the I-CSCF 640 a.

3)˜4) The I-CSCF 640 a obtains user information from the HSS 540 a inthe home network.

5) Next, the I-CSCF 640 a transmits the SIP-based REGISTER message tothe S-CSCF 630 a.

6)˜7) The S-CSCF 630 a obtains user information from the HSS.

8) Subsequently, the S-CSCF 630 a performs service control forregistration of the UE.

9)˜11) If the registration of the UE is successful, the S-CSCF 630 atransmits a 200 OK message.

<Structure of Next-Generation Mobile Communication>

With the success of Long Term Evolution (LTE)/LTE-Advanced (LTE-A) forthe 4th generation mobile communication, more interest is rising to thenext generation, i.e., 5th generation (also known as 5G) mobilecommunication and extensive research and development are being carriedout accordingly.

The 5G mobile communication defined in the InternationalTelecommunication Union (ITU) provides a data transfer rate of up to 20Gbps and a sensible transfer rate of at least 100 Mbps anytime anywhere.‘IMT-2020’ is a formal name, and aims to be commercialized in the year2020 worldwide.

The ITU proposes three usage scenarios, e.g., enhanced Mobile BroadBand(eMBB), massive Machine Type Communication (mMTC), and Ultra Reliableand Low Latency Communications (URLLC).

First, the URLLC relates to a usage scenario which requires a highreliability and a low latency. For example, a service such as autonomousdriving, factory automation, and augmented reality requires a highreliability and a low latency (e.g., a latency less than or equal to 1ms). At present, a latency of 4G (LTE) is statistically 21-43 ms (best10%), 33-75 ms (median). This is insufficient to support a servicerequiring the latency less than or equal to 1 ms.

Next, an eMBB usage scenario relates to a usage scenario requiring amobile ultra-wide band.

It seems that a core network designed for the existing LTE/LTE-A hasdifficulty in accommodating a high-speed service of the ultra-wide band.

Therefore, it is urgently required to re-design the core network in 5Gmobile communication.

FIG. 9 is a structural diagram of a next-generation mobile communicationnetwork.

5G Core (5GC) may include various components. In FIG. 9, 5GC includesAccess and mobility Management Function (AMF) 410, Session ManagementFunction (SMF) 420, Policy Control Function (PCF) 430, User PlaneFunction (UPF) 440, Application Function (AF) 450, Unified DataManagement (UDM) 460, and Non-3GPP InterWorking Function (N3IWF) 490,which correspond to some of them.

The UE 100 is connected to a data network through the UPF 450 through aNext Generation Radio Access Network (NG-RAN).

The UE 100 may be provided with a data service through untrustednon-3GPP access, e.g., Wireless Local Area Network (WLAN). To connectthe non-3GPP access to the core network, N3IWF 490 may be deployed.

FIG. 10 shows an example of an expected structure of next-generationmobile communication from a node perspective.

As can be seen with reference to FIG. 10, a UE is connected to a datanetwork (DN) via a next generation Radio Access Network (RAN).

The illustrated Control Plane Function (CPF) node performs functions ofthe entirety or part of a Mobility Management Entity (MME) of 4G mobilecommunication and control plane functions of the entirety or part of aServing Gateway (S-GW) and PDN gateway (P-GW) of 4G mobilecommunication. The CPF node includes an Access and mobility ManagementFunction (AMF) and a Session Management Function (SMF).

The illustrated User Plane Function (UPF) node is a type of a gatewaythrough which user data is transmitted/received. The UPF node mayperform user plane functions of the entirety or part of an S-GW or P-GWof 4G mobile communication.

The illustrated Policy Control Function (PCF) is a node which controls aprovider's policy.

The illustrated Application Function (AF) is a server for providingseveral services to the UE.

The illustrated Unified Data Management (UDM) is a type of a serverwhich manages subscriber information, like a Home Subscriber Server(HSS) of 4G mobile communication. The UDM stores the subscriberinformation in a Unified Data Repository (UDR) and manages it.

The illustrated Authentication Server Function (AUSF) authenticates andmanages the UE.

The illustrated Network Slice Selection Function (NSSF) is a node fornetwork slicing as described below.

In FIG. 10, the UE can simultaneously access two data networks by usingmultiple Protocol Data Unit (PDU) sessions.

FIG. 11 shows an example of an architecture for supporting simultaneousaccess to two data networks.

FIG. 11 shows an architecture for a UE to simultaneously access two datanetworks using one PDU session.

FIG. 12 is another exemplary diagram showing the structure of a radiointerface protocol between the UE and the gNB.

The radio interface protocol is based on the 3GPP radio access networkstandard. The radio interface protocol is horizontally composed of aphysical layer, a data link layer, and a network layer, and isvertically divided into a user plane for transmitting data informationand a control plane for transmitting a control signal.

The protocol layers may be divided into L1 (Layer 1), L2 (Layer 2), andL3 (Layer 3) based on the lower three layers of the Open SystemInterconnection (OSI) reference model widely known in communicationsystems.

Meanwhile, in FIG. 12, the RRC layer, the RLC layer, the MAC layer, andthe PHY layer located below the NAS layer are collectively referred toas an Access Stratum (AS).

<Problems to be Solved by the Disclosure of the Present Specification>

The present specification describes a situation in which a failureoccurs in the base station of the first PLMN by the first operator sothat the mobile communication service can no longer be provided throughthe corresponding base station. It is assumed that, temporarily (e.g.,hours or days, etc.) until the physical recovery of the correspondingbase station is made, the base station of the second PLMN by the secondoperator broadcasts SIB by including information on the first PLMN by athird party (i.e., the first operator) in order to provide services onbehalf of the first operator in the affected area.

In this case, the third-party subscription UE receiving the broadcastinformation accesses the network in the same way as accessing the HPLMN,whereas the network provides a form of servicing a roaming UE. That is,from a network point of view, in order to cope with a failure occurringin the first PLMN of the first operator, the network node of the secondPLMN (e.g., VPLMN) of the second operator connects to the network nodeof the first PLMN (e.g., HPLMN), and thus a route such as roaming ofHome Routed (HR) scheme can be used. This may cause the followingproblems.

It is assumed that the UE subscribed to the third PLMN of the thirdoperator performs roaming to the first PLMN of the first operator. SuchUE is referred to as an inbound roaming UE. Meanwhile, suppose that afailure has occurred in the first PLMN of the first operator. In thiscase, the second PLMN of the second operator transmits a SystemInformation Block (SIB) message including information on the first PLMNto cope with the failure of the first PLMN of the first operator. Whenthe inbound roaming UE receives the SIB message from the base station ofthe second PLMN, the inbound roaming UE recognizes that it has accessedthe base station of the first PLMN. In this case, various managementmethods may occur in the network depending on whether or not there is aroaming agreement between operators, but the inbound roaming UE may notbe aware of roaming to the second PLMN rather than the first PLMN. Thatis, the inbound roaming UE may send various requests to the networkwithout understanding the charging policy or roaming restrictions in thesecond PLMN.

Accordingly, if an appropriate operation of the network is notperformed, the utilization of network resources such as signaling wasteand the user's service experience may be lowered.

<Device to which the Disclosure of the Present Specification can beApplied>

Hereinafter, a device to which the disclosure of the presentspecification can be applied will be described.

FIG. 13 is a block diagram of a UE according to an embodiment.

As can be seen with reference to FIG. 13, A UE 100 includes a memory1010, a processor 1020, a transceiver 1031, a power management module1091, a battery 1092, a display 1041, an input unit 1053, a speaker1042, a microphone 1052, a Subscriber Identification Module (SIM) card,and one or more antennas.

The processor 1020 may be configured to implement the proposed function,process and/or method described in the present specification. Layers ofa wireless interface protocol may be implemented in the processor 1020.The processor 1020 may include Application-Specific Integrated Circuit(ASIC), other chipset, logical circuit and/or data processing apparatus.The processor 1020 may be an Application Processor (AP). The processor1020 may include at least one of a Digital Signal Processor (DSP), aCentral Processing Unit (CPU), a Graphics Processing Unit (GPU) and amodulator and demodulator (Modem). An example of the processor 1020 maybe SNAPDRAGON™ series processor manufactured by Qualcomm®, EXYNOS™series processor manufactured by Samsung®, A series processormanufactured by Apple®, HELIO™ series processor manufactured byMediaTek®, ATOM™ series processor manufactured by INTEL®, or thecorresponding next generation processor.

The power management module 1091 manages a power for the processor 1020and/or the transceiver 1031. The battery 1092 supplies power to thepower management module 1091. The display 1041 outputs the resultprocessed by the processor 1020. The input unit 1053 receives an inputto be used by the processor 1020. The input unit 1053 may be displayedon the display 1041. The SIM card is an integrated circuit used tosafely store International Mobile Subscriber Identity (IMSI) used foridentifying a subscriber in a mobile telephoning apparatus such as amobile phone and a computer and the related key. Many types of contactaddress information may be stored in the SIM card.

The memory 1010 is coupled with the processor 1020 in a way to operateand stores various types of information to operate the processor 1020.The memory may include Read-Only Memory (ROM), Random Access Memory(RAM), flash memory, a memory card, a storage medium, and/or otherstorage device. When the embodiment is implemented in software, thetechniques described in the present specification may be implemented ina module (e.g., process, function, etc.) for performing the functiondescribed in the specification. A module may be stored in the memory1010 and executed by the processor 1020. The memory may be implementedinside of the processor 1020. Alternatively, the memory 1010 may beimplemented outside of the processor 1020 and may be connected to theprocessor 1020 in communicative connection through various means whichis well-known in the art.

The transceiver 1031 is connected to the processor 1020 in a way tooperate and transmits and/or receives a radio signal. The transceiver1031 includes a transmitter and a receiver. The transceiver 1031 mayinclude a baseband circuit to process a radio frequency signal. Thetransceiver controls one or more antennas to transmit and/or receive aradio signal. In order to initiate a communication, the processor 1020transfers command information to the transceiver 1031 to transmit aradio signal that configures a voice communication data. When receivinga radio signal, the transceiver 1031 may transfer a signal to beprocessed by the processor 1020 and transform a signal in baseband. Theprocessed signal may be transformed into audible or readable informationoutput through the speaker 1042.

The speaker 1042 outputs a sound related result processed by theprocessor 1020. The microphone 1052 receives a sound related input to beused by the processor 1020.

A user inputs command information like a phone number by pushing (ortouching) a button of the input unit 1053 or a voice activation usingthe microphone 1052. The processor 1020 processes to perform a properfunction such as receiving the command information, calling a callnumber, and the like. An operational data on driving may be extractedfrom the SIM card or the memory 1010. Furthermore, the processor 1020may display the command information or driving information on thedisplay 1041 such that a user identifies it or for convenience.

FIG. 14 is a block diagram showing the configuration of a UE shown inFIG. 13 in more detail.

The terminal 100 may include a transceiver unit 1030, a processor 1020,a memory 1030, a sensing unit 1060, an output unit 1040, an interfaceunit 1090, an input unit 1050, and a power supply unit 1080, etc. Sincethe components shown in FIG. 14 are not essential for implementing theterminal, the terminal described in this specification may have more orfewer components than those listed above.

More specifically, among the components, the transceiver 1030 includeone or more modules that enable wireless communication between theterminal 100 and the wireless communication system, between the terminal100 and another terminal 100, or between the terminal 100 and anexternal server. In addition, the transceiver 1030 may include one ormore modules for connecting the terminal 100 to one or more networks.

The transceiver 1030 may include at least one of a broadcast receiver1032, a mobile communication transceiver 1031, a wireless Internettransceiver 1033, a short-range communication unit 1034, and a locationinformation receiver 1035.

The input unit 1050 includes a camera 1051 or an image input unit forinputting an image signal, a microphone 1052 or an audio input unit forinputting an audio signal, and a user input unit 1053 for receivinginformation from a user, for example, a touch key, a push key(mechanical key), etc. The voice data or image data collected by theinput unit 1050 may be analyzed and processed as a user's controlcommand.

The sensing unit 1060 may include one or more sensors for sensing atleast one of information in the mobile terminal, surrounding environmentinformation surrounding the mobile terminal, and user information. Forexample, the sensing unit 1060 may include a proximity sensor 1061, anillumination sensor 1062, an illumination sensor, a touch sensor, anacceleration sensor, a magnetic sensor, gravity Sensor (G-sensor),gyroscope sensor, motion sensor, RGB sensor, infrared sensor (IR sensor:infrared sensor), fingerprint sensor (finger scan sensor), ultrasonicsensor, optical sensors (e.g., cameras 1051), microphones 1052, batterygauges, environmental sensors (e.g., barometers, hygrometers,thermometers, radiation sensors, It may include at least one of athermal sensor, a gas sensor, etc.) and a chemical sensor (e.g., anelectronic nose, a healthcare sensor, a biometric sensor, etc.).Meanwhile, the mobile terminal disclosed in the present specificationmay combine and utilize information sensed by at least two or more ofthese sensors.

The output unit 1040 is for generating an output related to visual,auditory or tactile sense, the output unit 1040 may include at least oneof a display unit 1041, a sound output unit 1042, a haptic output unit1043, and an optical output unit 1044. The display unit 1041 mayimplement a touch screen by forming a layer structure with the touchsensor each other or integrally formed with the touch sensor. Such atouch screen may function as a user input unit 1053 that provides aninput interface between the terminal 100 and a user, and may provide anoutput interface between the terminal 100 and a user.

The interface unit 1090 serves as a passage with various types ofexternal devices connected to the terminal 100. This interface unit 1090may include at least one of a wired/wireless headset port (port), anexternal charger port (port), a wired/wireless data port (port), amemory card (memory card) port, a port connecting a device equipped withan identification module, an audio input/output (I/O) port, a videoinput/output (I/O) port, and an earphone port. Corresponding to theconnection of the external device to the interface unit 1090, theterminal 100 may perform appropriate control related to the connectedexternal device.

In addition, the memory 1030 stores data supporting various functions ofthe terminal 100. The memory 1030 may store a plurality of applicationprograms (or applications) driven in the terminal 100, data foroperation of the terminal 100, and commands At least some of theseapplication programs may be downloaded from an external server throughwireless communication. Also, at least some of these applicationprograms may exist on the terminal 100 from the time of shipment forbasic functions (eg, functions for incoming calls, outgoing functions,message reception, and message outgoing functions) of the terminal 100.Meanwhile, the application program may be stored in the memory 1030,installed on the terminal 100, and driven by the processor 1020 toperform an operation (or function) of the mobile terminal.

The processor 1020 generally controls the overall operation of theterminal 100 in addition to the operation related to the applicationprogram. The processor 1020 may provide or process appropriateinformation or functions to a user by processing signals, data,information, etc. input or output through the above-described componentsor by driving an application program stored in the memory 1030.

In addition, the processor 1020 may control at least some of theaforementioned components in order to drive an application programstored in the memory 1030. Furthermore, the processor 1020 may operateby combining at least two or more of the components included in theterminal 100 to drive the application program.

The power supply unit 1080 receives external power and internal powerunder the control of the processor 1020 to supply power to eachcomponent included in the terminal 100. The power supply unit 1080includes a battery, and the battery may be a built-in battery or areplaceable battery.

At least some of the respective components may operate in cooperationwith each other to implement an operation, control, or control method ofa mobile terminal according to various embodiments to be describedbelow. In addition, the operation, control, or control method of themobile terminal may be implemented on the mobile terminal by driving atleast one application program stored in the memory 1030.

Hereinafter, before looking at various embodiments implemented throughthe terminal 100 as described above, the above-listed components will bedescribed in more detail with reference to the drawings.

First, referring to the transceiver 1030, the broadcast receiver 1032 ofthe transceiver 1030 receives a broadcast signal and/or broadcastrelated information from an external broadcast management server througha broadcast channel The broadcast channel may include a satellitechannel and a terrestrial channel Two or more of the broadcast receptionmodules may be provided to the mobile terminal 100 for simultaneousbroadcast reception or broadcast channel switching for at least twobroadcast channels.

The mobile communication transceiver 1031 transmit and receive wirelesssignal with at least one of a base station, an external terminal, and aserver on a mobile communication network constructed according to thetechnical standards or communication methods for mobile communication(e.g., Global System for Mobile communication (GSM), Code Division MultiAccess (CDMA), Code Division Multi Access 2000 (CDMA2000), EnhancedVoice-Data Optimized or Enhanced Voice-Data Only (EV-DO), Wideband CDMA(WCDMA), High Speed Downlink Packet Access (HSDPA), High Speed UplinkPacket Access (HSUPA), Long Term Evolution (LTE), LTE Advanced (LTE-A),3GPP New Radio access technology (NR), etc.).

The wireless signal may include various types of data according totransmission and reception of a voice call signal, a video call signal,or a text/multimedia message.

The wireless Internet transceiver 1033 refers to a module for wirelessInternet access, and may be built-in or external to the terminal 100.The wireless Internet transceiver 1033 is configured to transmit andreceive wireless signals in a communication network according towireless Internet technologies.

As wireless Internet technologies, for example, Wireless LAN (WLAN),Wi-Fi, Wi-Fi Direct, Digital Living Network Alliance (DLNA), WiBro,WiMAX, HSDPA, HSUPA, LTE, LTE-A, 3GPP NR, and the like. The Internettransceiver 1033 transmits and receives data according to at least onewireless Internet technology within a range including Internettechnologies not listed above.

From the point of view that wireless Internet access by WiBro, HSDPA,HSUPA, GSM, CDMA, WCDMA, LTE, LTE-A, 3GPP NR, etc., is made through amobile communication network, the wireless Internet transceiver 1033performing wireless Internet access through the mobile communicationnetwork may be understood as a type of the mobile communicationtransceiver 1031.

The short-range communication unit 1034 is for short-rangecommunication, and may support short-distance communication by using atleast one of Bluetooth™, Radio Frequency Identification (RFID), InfraredData Association (IrDA), Ultra Wideband (UWB), ZigBee, Near FieldCommunication (NFC), Wi-Fi, Wi-Fi Direct, and Wireless Universal SerialBus (USB) technologies. The short-distance communication unit 1034 maysupport wireless communication between the terminal 100 and the wirelesscommunication system, between the terminal 100 and the other terminal100, or between the terminal 100 and another network in which the otherterminal (100, or external server) is located. The local area networkmay be wireless personal area networks.

Here, the other terminal 100 may be a wearable device capable ofexchanging (or interworking) data with the terminal 100, e.g., a smartwatch, a smart glass, neckband, Head Mounted Display (HMD). Theshort-range communication unit 1034 may detect (or recognize) a wearabledevice capable of communicating with the terminal 100 in the vicinity ofthe terminal 100. Furthermore, when the detected wearable device is adevice authenticated to communicate with the terminal 100, the processor1020 may transmit at least a portion of data processed by the terminal100 to a wearable device through the short-range communication unit1034. Accordingly, the user of the wearable device may use dataprocessed by the terminal 100 through the wearable device. For example,according to this, when a call is received in the terminal 100, it ispossible for the user to perform a phone call through the wearabledevice. When a message is received in the terminal 100, it is possiblefor the user to check the received message through the wearable device.

Furthermore, screen mirroring with a TV located in the house or adisplay inside a car is performed through the short-distancecommunication unit 1034, and a corresponding function is performed basedon, for example, the MirrorLink or Miracast standard. In addition, it isalso possible to directly control a TV or a display inside a vehicle byusing the terminal 100.

The location information module 1035 is a module for acquiring alocation (or current location) of a mobile terminal, and arepresentative example thereof includes a Global Positioning System(GPS) module or a Wireless Fidelity module. For example, if the mobileterminal utilizes a GPS module, it can acquire the location of themobile terminal by using a signal transmitted from a GPS satellite. Asanother example, if the mobile terminal utilizes the Wi-Fi module, thelocation of the mobile terminal may be obtained based on information ofthe Wi-Fi module and a wireless Access Point (AP) that transmits orreceives a wireless signal. If necessary, the location informationmodule 1035 may perform any function of the other modules of thetransceiver 1030 to obtain data on the location of the mobile terminalas a substitute or additionally. The location information module 1035 isa module used to obtain the location (or current location) of the mobileterminal, and is not limited to a module that directly calculates orobtains the location of the mobile terminal.

Each of the broadcast receiver 1032, the mobile communicationtransceiver 1031, the short-range communication unit 1034, and thelocation information module 1035 may be implemented as a separate moduleperforming a corresponding function, and functions corresponding to twoor more of the transceiver 1031, the short-range communication unit1034, and the location information module 1035 may be implemented by onemodule.

Next, the input unit 1050 is for inputting image information (orsignal), audio information (or signal), data, or information input froma user, for input of image information, the terminal 100 may be providedwith one or a plurality of cameras 1051. The camera 1051 processes animage frame such as a still image or a moving image obtained by an imagesensor in a video call mode or a photographing mode. The processed imageframe may be displayed on the display unit 1041 or stored in the memory1030. On the other hand, the plurality of cameras 1051 provided in theterminal 100 may be arranged to form a matrix structure, and through thecameras 1051 forming the matrix structure as described above, imageinformation may be input to the terminal 100 has a plurality of camerashaving various angles or focal points. In addition, the plurality ofcameras 1051 may be arranged in a stereo structure to acquire a leftimage and a right image for realizing a stereoscopic image.

The microphone 1052 processes an external sound signal as electricalvoice data. The processed voice data may be utilized in various waysaccording to a function (or a running application program) beingperformed by the terminal 100. Meanwhile, various noise removalalgorithms for removing noise generated in the process of receiving anexternal sound signal may be implemented in the microphone 1052.

The user input unit 1053 is for receiving information from a user, andwhen information is input through the user input unit 1053, theprocessor 1020 may control the operation of the terminal 100 tocorrespond to the input information. The user input unit 1053 is amechanical input means (or a mechanical key, for example, a buttonlocated on the front, rear or side of the terminal 100, a dome switch, ajog wheel, a jog switch, etc.) and a touch input means. As an example,the touch input means consists of a virtual key, a soft key, or a visualkey displayed on the touch screen through software processing, orconsists of a touch key (touch key) disposed on a part other than thetouch screen. On the other hand, the virtual key or the visual key, ispossible to be displayed on the touch screen while having various forms,for example, graphic, text, icon, video or a combination of these forms.

Meanwhile, the sensing unit 1060 senses at least one of information inthe mobile terminal, surrounding environment information surrounding themobile terminal, and user information, and generates a sensing signalcorresponding thereto. The processor 1020 may control the driving oroperation of the terminal 100 or perform data processing, functions, oroperations related to an application program installed in the terminal100 based on the sensing signal. Representative sensors among varioussensors that may be included in the sensing unit 1060 will be describedin more detail.

First, the proximity sensor 1061 refers to a sensor that detects thepresence or absence of an object approaching a predetermined detectionsurface or an object existing in the vicinity without mechanical contactusing the force of an electromagnetic field or infrared rays. Theproximity sensor 1061 may be disposed in an inner region of the mobileterminal covered by the touch screen described above or in the vicinityof the touch screen.

Examples of the proximity sensor 1061 include a transmission typephotoelectric sensor, a direct reflection type photoelectric sensor, amirror reflection type photoelectric sensor, a high frequencyoscillation type proximity sensor, a capacitive type proximity sensor, amagnetic type proximity sensor, an infrared proximity sensor, and thelike. In the case where the touch screen is capacitive, the proximitysensor 1061 may be configured to detect the proximity of an objecthaving conductivity as a change in an electric field according to theproximity of the object. In this case, the touch screen (or touchsensor) itself may be classified as a proximity sensor.

On the other hand, for convenience of description, the act ofapproaching an object on the touch screen without being in contact sothat the object is recognized that it is located on the touch screen iscalled “proximity touch”, and the act of actually touching an object onthe screen is called “contact touch”. The position where the object istouched in proximity on the touch screen means a position where theobject is perpendicular to the touch screen when the object is touchedin proximity. The proximity sensor 1061 may detect a proximity touch anda proximity touch pattern (e.g., proximity touch distance, proximitytouch direction, proximity touch speed, proximity touch time, proximitytouch position, proximity touch movement state, etc.). On the otherhand, the processor 1020 processes data (or information) correspondingto the proximity touch operation and the proximity touch patterndetected through the proximity sensor 1061 as above, and further, printvisual information corresponding to the processed data on the touchscreen. Furthermore, the processor 1020 may control the terminal 100 toprocess different operations or data (or information) according towhether a touch to the same point on the touch screen is a proximitytouch or a contact touch.

The touch sensor detects a touch (or touch input) applied to the touchscreen (or the display unit 1041) using at least one of various touchmethods such as a resistive film method, a capacitive method, aninfrared method, an ultrasonic method, and a magnetic field method, etc.

As an example, the touch sensor may be configured to convert a change inpressure applied to a specific part of the touch screen or a change incapacitance occurring in a specific part of the touch screen into anelectrical input signal. The touch sensor may be configured to detect aposition in which a touch object applying a touch on the touch screen,an area, a pressure at the time of touch, an electrostatic capacitanceat the time of touch, etc. Here, the touch object is an object thatapplies a touch to the touch sensor, and may be, for example, a finger,a touch pen or a stylus pen, a pointer, or the like.

As such, when there is a touch input to the touch sensor, a signal(s)corresponding thereto is sent to the touch controller. The touchcontroller processes the signal(s) and then sends the corresponding datato the processor 1020. Accordingly, the processor 1020 may know whicharea of the display unit 1041 has been touched, and the like. Here, thetouch controller may be a component separate from the processor 1020, ormay be the processor 1020 itself.

Meanwhile, the processor 1020 may perform different controls or mayperform the same control according to the type of the touch object thattouches the touch screen (or a touch key provided other than the touchscreen). Whether to perform different control or the same controlaccording to the type of the touch object may be determined according tothe current operating state of the terminal 100 or a running applicationprogram.

On the other hand, the touch sensor and the proximity sensor describedabove are independently or in combination, may sense various types oftouch such as, a short (or tap) touch, a long touch, a multi touch, anda drag touch, flick touch, pinch-in touch, pinch-out touch, swipe touch,hovering touch, etc.

The ultrasonic sensor may recognize location information of a sensingtarget by using ultrasonic waves. Meanwhile, the processor 1020 maycalculate the position of the wave source based on information sensed bythe optical sensor and the plurality of ultrasonic sensors. The positionof the wave source may be calculated using the property that light ismuch faster than ultrasonic waves, that is, the time at which lightreaches the optical sensor is much faster than the time at whichultrasonic waves reach the ultrasonic sensor. More specifically, theposition of the wave source may be calculated by using a time differencefrom the time that the ultrasonic wave arrives using light as areference signal.

On the other hand, the camera 1051 as described in terms of thecomponents of the input unit 1050 includes at least one of a camerasensor (e.g., CCD, CMOS, etc.), a photo sensor (or an image sensor), anda laser sensor.

The camera 1051 and the laser sensor may be combined with each other todetect a touch of a sensing target for a 3D stereoscopic image. Thephoto sensor may be stacked on the display device, and the photo sensoris configured to scan the motion of the sensing target close to thetouch screen. More specifically, the photo sensor mounts photo diodesand transistors (TRs) in rows/columns and scans the contents placed onthe photo sensors using electrical signals that change according to theamount of light applied to the photo diodes. That is, the photo sensorcalculates the coordinates of the sensing target according to the amountof change in light, and through this, location information of thesensing target can be obtained.

The display unit 1041 displays (outputs) information processed by theterminal 100. For example, the display unit 1041 may display executionscreen information of an application program driven in the terminal 100or User Interface (UI) and Graphic User Interface (GUI) informationaccording to the execution screen information.

Also, the display unit 1041 may be configured as a stereoscopic displayunit for displaying a stereoscopic image.

A three-dimensional display method such as a stereoscopic method(glasses method), an auto stereoscopic method (glasses-free method), ora projection method (holographic method) may be applied to thestereoscopic display unit.

The sound output unit 1042 may output audio data received from thetransceiver 1030 or stored in the memory 1030 in a call signalreception, a call mode or a recording mode, a voice recognition mode, abroadcast reception mode, and the like. The sound output unit 1042 alsooutputs a sound signal related to a function (e.g., a call signalreception sound, a message reception sound, etc.) performed in theterminal 100. The sound output unit 1042 may include a receiver, aspeaker, a buzzer, and the like.

The haptic module 1530 generates various tactile effects that the usercan feel. A representative example of the tactile effect generated bythe haptic output unit 1043 may be vibration. The intensity and patternof vibration generated by the haptic output unit 1043 may be controlledby a user's selection or setting of a processor. For example, the hapticoutput unit 1043 may synthesize and output different vibrations oroutput them sequentially.

In addition to vibration, the haptic output unit 1043 may generatevarious tactile effects such as a pin arrangement that moves verticallywith respect to the contact skin surface, a jet or suction force of airthrough a nozzle or an inlet, a touch on the skin surface, contact of anelectrode, an electrostatic force, effect caused by heat absorption andthe effect of reproducing a feeling of coolness and warmth using anelement capable of absorbing heat or generating heat, etc.

The haptic output unit 1043 may not only deliver a tactile effectthrough direct contact, but may also be implemented so that the user canfeel the tactile effect through a muscle sensation such as a finger orarm. Two or more haptic output units 1043 may be provided according tothe configuration of the terminal 100.

The light output unit 1044 outputs a signal for notifying the occurrenceof an event by using the light of the light source of the terminal 100.Examples of the event generated in the terminal 100 may be messagereception, call signal reception, missed call, alarm, schedulenotification, email reception, information reception through anapplication, and the like.

The signal output from the optical output unit 1044 is implemented asthe mobile terminal emits light of a single color or a plurality ofcolors toward the front or rear side. The signal output may beterminated when the mobile terminal detects the user's eventconfirmation.

The interface unit 1090 serves as a passage with all external devicesconnected to the terminal 100. The interface unit 1090 receives datafrom an external device, receives power and transmits it to eachcomponent inside the terminal 100, or allows data inside the terminal100 to be transmitted to an external device. For example, awired/wireless headset port, an external charger port, a wired/wirelessdata port, a memory card port, a port for connecting a device equippedwith an identification module (port), an audio I/O port, a video I/Oport, an earphone port, etc. may be included in the interface unit 1090.

On the other hand, the identification module is a chip storing variousinformation for authenticating the use authority of the terminal 100,the identification module may include a User Identification Module(UIM), a Subscriber Identification Module (SIM), a Universal SubscriberIdentification Module (USIM) and the like. A device equipped with anidentification module (hereinafter, ‘identification device’) may bemanufactured in the form of a smart card. Accordingly, theidentification device may be connected to the terminal 100 through theinterface unit 1090.

In addition, the interface unit 1090 may be a path through which powerfrom the cradle is supplied to the terminal 100 when the terminal 100 isconnected to an external cradle, or a path through which variouscommands signal input from the cradle by the user transmitted to theterminal 100. Various command signals or the power input from the cradlemay be operated as signals for recognizing that the terminal 100 iscorrectly mounted on the cradle.

The memory 1030 may store a program for the operation of the processor1020, and may temporarily store input/output data (e.g., a phone book, amessage, a still image, a moving image, etc.). The memory 1030 may storedata related to vibrations and sounds of various patterns output when atouch input is performed on the touch screen.

The memory 1030 may include at least one type of storage medium such asa flash memory type, a hard disk type, a Solid State Disk (SSD) type, aSilicon Disk Drive (SDD) type, and a multimedia card micro type,card-type memory (such as SD or XD memory), Random Access Memory (RAM),Static Random Access Memory (SRAM), Read-Only Memory (ROM), ElectricallyErasable Programmable Read-Only Memory (EEPROM), a ProgrammableRead-Only Memory (PROM), a magnetic memory, a magnetic disk, and anoptical disk. The terminal 100 may be operated in relation to a webstorage that performs a storage function of the memory 1030 on theInternet.

Meanwhile, as described above, the processor 1020 controls the operationrelated to the application program and the general operation of theterminal 100 in general. For example, if the state of the mobileterminal satisfies a set condition, the processor 1020 may execute orrelease a lock state that restricts input of a user's control command toapplications.

In addition, the processor 1020 may perform control and processingrelated to voice calls, data communication, video calls, etc., orperform pattern recognition processing capable of recognizinghandwriting input or drawing input performed on the touch screen as textand images, respectively. Furthermore, the processor 1020 may controlany one or a plurality of the components described above in combinationto implement various embodiments described below on the terminal 100.

The power supply unit 1080 receives external power and internal powerunder the control of the processor 1020 to supply power necessary foroperation of each component. The power supply unit 1080 includes abattery, and the battery may be a built-in battery configured to berechargeable, and may be detachably coupled to the terminal body forcharging or the like.

In addition, the power supply unit 1080 may include a connection port,and the connection port may be configured as an example of the interface1090 to which an external charger that supplies power for charging thebattery is electrically connected.

As another example, the power supply unit 1080 may be configured tocharge the battery in a wireless manner without using the connectionport. In this case, power can be transmitted to the power supply unit1080 uses one or more of an inductive coupling method based on amagnetic induction phenomenon or a resonance coupling method based on anelectromagnetic resonance phenomenon from an external wireless powertransmitter.

Meanwhile, various embodiments below may be implemented in, for example,a computer-readable recording medium using software, hardware, or acombination thereof.

On the other hand, the mobile terminal can be extended to a wearabledevice that can be worn on the body beyond the dimension that the usermainly holds in the hand. Such wearable devices include a smart watch,smart glass, and (HMD and the like. Hereinafter, examples of mobileterminals extended to wearable devices will be described.

The wearable device may be configured to be able to exchange (orinterwork) data with another terminal 100. The short-range communicationunit 1034 may detect (or recognize) a wearable device capable ofcommunicating around the terminal 100. Furthermore, when the detectedwearable device is a device authenticated to communicate with theterminal 100, the processor 1020 may transmit at least a portion of dataprocessed in the terminal 100 to the wearable device through theshort-range communication unit 1034. Accordingly, the user may use dataprocessed by the terminal 100 through the wearable device. For example,it is possible to perform a phone call through the wearable device whena call is received in the terminal 100, or to check the received messagethrough the wearable device when a message is received to the terminal100.

<Disclosure of the Present Specification>

The disclosure of the present specification may be implemented by acombination of one or more of the following configurations. In the caseof the embodiment below, an embodiment is shown to show each individualconfiguration, but an embodiment in which one or more combinations areconfigured together may be implemented.

Hereinafter, an EPS-based embodiment will be described, but the contentdisclosed by the present specification is also applicable to anembodiment implemented in 5GS.

In the present specification, a special roaming situation mode of the UE(i.e., not a normal roaming situation, but a roaming situation thatoperates to overcome the failure situation as described above) isdefined. For ease of description in the present specification, generalroaming will be referred to as N-roaming, and roaming that operates toovercome the failure situation will be referred to as Special roaming(S-roaming) or Emergency roaming (E-roaming)

As described in the above problem, if the UE does not understand theS-roaming or E-roaming (i.e., roaming operation to overcome a failuresituation) situation, it recognizes it as a non-roaming situation andoperates. If the UE recognizes the S-roaming situation through themethods described below, the UE may operate in the S-roaming mode presetby the operator. The operator's settings may be pre-configured ortransmitted to the UE through an Open Mobile Alliance (OMA)-DeviceManagement (DM) scheme or a policy delivery scheme. The operator'ssettings may be updated as necessary.

For example, in the S-roaming situation, the operator may set theinbound roaming UE to allow requests for voice and SMS, but limit dataservice requests. In addition, the operator may set the priority ofrandom access by a specific application of the inbound roaming UEdifferently from the general situation. Alternatively, for the purposeof adjusting the signal load, the operator may change the period of thePeriodic Tracking Area Update (P-TAU) of the UE, or may set thenon-essential request from the periodic operation of the UE to bedelayed.

I. A Method for Supporting an Inbound Roaming UE in a Failure Situation

I-1. Network Behavior

The inbound roaming UE (i.e., the subscriber of the third PLMN)recognizes that the access request message has been sent to the networkof the first PLMN via the base station of the first PLMN (In general,since roaming of the first PLMN is set to be prioritized according tothe roaming agreement, information on the first PLMN may be received andpreferentially attempted to access the first PLMN). However, actually,the access request message of the inbound roaming UE is transmitted tothe network of the second PLMN via the base station of the second PLMNthat is instead temporarily transmitting information on the first PLMN.

1-1-A. A Method of Inducing Access to Another PLMN by Rejecting anAccess Request from an Inbound Roaming UE

According to the roaming agreement among the operator of the first PLMN,the operator of the second PLMN, and the operator of the third PLMN, thenetwork node receiving the access request from the inbound roaming UEmay reject the access of the UE by using a cause field in the NASmessage, etc. In this case, the cause field or another field in the NASmessage may explicitly or implicitly indicate that S-roaming (i.e.,roaming to overcome a failure situation) can be performed.

When the UE performs an operation for selecting another PLMN, thenetwork node may transmit additional information to preferentiallyprefer the second PLMN or a specific PLMN.

In addition, the information may be temporary information so that the UEcan select the first PLMN again in another region/after a certain timeperiod. That is, the network node may specify that the information istemporary information. That is, even if another PLMN is selected fromthe viewpoint of the UE, if the region/time information is changed, thepriority of the previous PLMN selection may be followed again.

I-1-B. A Method for Accommodating the Access Request of the UE

I-1-B-1. When there is a roaming agreement between the operator of thesecond PLMN and the operator of the third PLMN

According to the roaming agreement among the operator of the first PLMN,the operator of the second PLMN, and the operator of the third PLMN, thenetwork node of the second PLMN may not create a route of a Home Routed(HR) roaming scheme to the network node of the first PLMN. Instead, thenetwork node of the second PLMN performs operations for directlyproviding a service.

In addition, the network node of the second PLMN may perform operationsfor reallocation of the network node and change of the base station inorder to perform optimal service.

The network node of the second PLMN informs the UE that it is connectedto the second PLMN. In this case, the network node of the second PLMNmay provide information on the failure status of the first PLMN orinformation on the possibility of occurrence of the S-roaming situationto the UE. The information may be utilized later when the UE selects orreselects a PLMN. Additionally, the information may be set as temporaryinformation so that the UE can select the first PLMN again in anotherregion/after a certain period of time. That is, the network node of thesecond PLMN may inform the UE that the information is temporaryinformation.

According to the roaming agreement, since the service provided by thesecond PLMN may be limited compared to the service provided by the firstPLMN, this information may be provided to the UE. The information may bedelivered to the UE through a NAS message, or may be delivered through apop-up window, etc., after a successful connection to the SMS/MMS andserver access of a specific application service.

I-1-B-2. When there is no roaming agreement between the second PLMN andthe third PLMN (however, in order to cope with the occurrence of afailure of the first PLMN, there is an agreement between the first PLMNand the third PLMN for a countermeasure for failure (using the secondPLMN))

According to the roaming agreement between the operator of the firstPLMN, the operator of the second PLMN, and the operator of the thirdPLMN, the network node of the second PLMN may create a route of HRscheme to the network node of the first PLMN, and perform operations toprovide a service to the inbound roaming UE.

Additionally, for authentication of subscribers without a roamingagreement, the second PLMN network node may perform authentication viathe network node of the first PLMN. Alternatively, even if there is noroaming service agreement, a business agreement can be made in advanceto access the mutual subscriber information Data Base (DB) in thesespecial obstacles.

When generating charging data of the network, since the service is notsimply provided through the first PLMN, charging information for theservice through the second PLMN may be explicitly collected and notifiedto the third PLMN.

The network may perform different policies for services provided perPLMN.

The network node of the second PLMN informs the UE that it is connectedto the second PLMN. In this case, the network node of the second PLMNmay provide information on the failure status of the first PLMN orinformation on the possibility of occurrence of the S-roaming situationto the UE. The information may be utilized later when the UE selects orreselects a PLMN. Additionally, the information may be set as temporaryinformation so that the UE can select the first PLMN again in anotherregion/after a certain period of time. That is, the network node of thesecond PLMN may inform the UE that the information is temporaryinformation.

According to the roaming agreement, since the service provided by thesecond PLMN may be limited compared to the service provided by the firstPLMN, this information may be provided to the UE. The information may bedelivered to the UE through a NAS message, or may be delivered through apop-up window, etc., after a successful connection to the SMS/MMS andserver access of a specific application service.

FIG. 15 is an exemplary diagram illustrating a screen of a UE accordingto an embodiment.

Referring to FIG. 15, when roaming is performed to cope with the failuresituation as described above, unlike the roaming icon generallydisplayed, the processor of the UE may display an icon 1041-12 forindicating a corresponding situation (i.e., a situation in whichS-roaming or E-roaming is performed to cope with the failure situation)on a status bar displayed on the display unit 1041. The icon 1041-12 mayindicate that it has been switched to the roaming mode to cope with thefailure situation or may mean that a specific roaming policy is applied.The icon 1041-12 may be an ER indicating emergency roaming or an SRindicating special roaming.

The icon 1041-12 may have a different shape from a general icon (i.e.,an icon indicating a state of simply receiving information orrecognizing such a state). Alternatively, although the shape is thesame, the display shape may be different. For example, the icon 1041-12may be displayed while blinking, but the general icon may be displayedwithout blinking.

Meanwhile, various icons representing different information may bedisplayed on the display unit 1041. In addition, as described above,these various icons may be differently changed in shape, form (e.g.,blinking), color, etc., of the display (e.g., icon, notification window,etc.) according to the recognition of the UE and the application levelof the roaming mode.

In addition, information 1041-13 indicating the signal strength from thebase station of the second PLMN may be displayed on the status bardisplayed on the display unit 1041 according to roaming to cope with thefailure situation.

Also, information 1041-11 indicating that the service of the first PLMNis impossible (e.g., No Service) may be displayed on the status bardisplayed on the display unit 1041.

FIG. 16 is an exemplary diagram illustrating a screen of a UE accordingto an embodiment.

When the UE is successfully connected to the network, the UE may displaya message 1041-14 on the display unit 1041 indicating that roaming hasbeen performed to cope with a failure situation. That is, the UE maydisplay the message 1041-14 received from the server on the display unit1041. In this case, information on available services (e.g., a list ofvoice calls, text services, and limited data services, etc.) may bedisplayed in the message 1041-14 along with a description of thecorresponding roaming mode situation. Here, in the message 1041-14, ahyperlink 1041-15 for notifying detailed information, such as thecontent of each service, may be displayed. When the hyperlink 1041-15 isselected (e.g., when the hyperlink 1041-15 is touched by the user), aconnection to a server capable of providing the corresponding content isperformed. That is, a PDN connection request from the UE to thecorresponding server may occur.

In addition, information 1041-13 indicating the signal strength from thebase station of the second PLMN may be displayed on the status bardisplayed on the display unit 1041 according to roaming Also,information 1041-11 indicating that the service of the first PLMN isimpossible (e.g., No Service) may be displayed on the status bardisplayed on the display unit 1041.

I-2. UE Operation

The UE recognizes the S-roaming situation based on the informationreceived from the network node.

The UE (if necessary) performs PLMN selection again.

In managing the priority of roaming PLMN selection, the UE manages thePLMN for S-roaming received from the network node and temporaryrejection by the network node, in addition to general prioritymanagement.

The UE performs an operation of switching to the S-roaming mode orapplying the policy of the S-roaming mode according to a preset operatorpolicy.

As described above, when the UE recognizes the S-roaming situation, theUE may display information for notifying the S-roaming.

FIG. 17 is an exemplary diagram illustrating a screen of a UE.

Referring to FIG. 17, the UE may display a message 1041-16 indicatingthat roaming has been performed to cope with a failure situation on thedisplay unit 1041.

In addition, information 1041-13 indicating the signal strength from thebase station of the second PLMN may be displayed on the status bardisplayed on the display unit 1041 according to roaming Also,information 1041-11 indicating that the service of the first PLMN isimpossible (e.g., No Service) may be displayed on the status bardisplayed on the display unit 1041.

Meanwhile, information on available services may be displayed in themessage 1041-16 along with a description of the corresponding roamingSpecifically, the message may indicate that only voice calls, textservices, and limited data services are available, and other servicesare unavailable.

FIG. 18. is an exemplary diagram illustrating applications of a UE.

As can be seen with reference to FIG. 18, when S-roaming or E-roaming isperformed to cope with a failure situation, the UE may operate in apredetermined mode for S-roaming or E-Roaming, e.g., a safe modeprovided by Microsoft's Windows. The screen according to thepredetermined operation mode may have different resolution, color, andfont like the safe mode screen of a Windows PC.

Specifically, when S-roaming or E-roaming is performed to cope with afailure situation, the UE may not display icons of all installedapplications, but only display icons of executable applications (e.g., aphone application and a text message application). That is, icons ofnon-executable applications may not be displayed at all. Alternatively,icons of non-executable applications may be displayed in shades or blackand white or transparent, while icons of executable applications may bedisplayed in color.

In addition, the UE may display a preset background screen image insteadof a background screen image designated by the user. Alternatively, asshown, the UE may display information indicating that only a limitedservice is available in the background screen image.

If the user executes the phone application, the UE may display a screenas shown in FIG. 18.

FIG. 19 is an exemplary diagram illustrating a screen displayed by aphone application executed in a UE.

Referring to FIG. 19, information 1041-16 indicating that roaming hasbeen performed in order to cope with a failure situation may bedisplayed on a screen displayed by a phone application executed in theUE.

That is, a guide saying that the emergency roaming to a third party hasbeen performed due to a failure situation may be displayed on the screendisplayed by the phone application executed in the UE.

Also, an icon 1041-12 indicating that roaming has been performed to copewith a failure situation may be displayed on the status bar displayed onthe display unit 1041.

In addition, information 1041-13 indicating the signal strength from thebase station of the second PLMN may be displayed on the status bardisplayed on the display unit 1041 according to roaming

Also, information 1041-11 indicating that the service of the first PLMNis impossible (e.g., No Service) may be displayed on the status bardisplayed on the display unit 1041.

If an application other than the phone call and message is executed bythe user, the screen of the corresponding application may display anotification message, a pop-up message, or a guide message informingthat the application is unavailable.

Meanwhile, as described above, the predetermined mode for S-roaming orE-roaming may be applied when set by a user as described below.

FIG. 20 is an exemplary diagram illustrating a setting screen of a UE.

As shown in FIG. 20, when the service is unavailable due to a failure ofthe first PLMN, after roaming to the second PLMN, the UE may display ascreen for receiving input of a user's setting as to whether to use alimited service. When the user inputs permission, and when the firstPLMN becomes unavailable due to a failure, a screen may be displayed asshown in FIGS. 15 to 19.

FIG. 21 is a detailed block diagram of a processor of a UE forimplementing the examples shown in FIGS. 15 to 20.

As can be seen with reference to FIG. 21, the processor 1020 of the UEmay include a configuration unit 1020-1, a roaming awareness unit1020-2, and a screen display unit 1020-3.

The configuration unit 1020-1 receives and stores a user's setting as towhether or not to use a limited service as shown in FIG. 20, whenroaming to the second PLMN is performed because the first PLMN isunavailable due to a failure.

The roaming awareness unit 1020-2 recognizes whether or not roaming tothe second PLMN is performed when the service is unavailable in thefirst PLMN due to a failure.

The screen display unit 1020-3 may display a screen as shown in FIGS. 15to 19.

FIG. 22a and FIG. 22b show an embodiment in which the disclosure of thepresent specification is applied to EPS.

In FIG. 22a and FIG. 22 b, it is assumed that there is a roamingagreement between the first PLMN and the third PLMN, and a subscriber ofthe third PLMN can access the first PLMN to receive a roaming service.

In addition, in FIG. 22a and FIG. 22 b, it is assumed that acommunication service is impossible due to a communication disaster inthe first PLMN, and the base station of the second PLMN temporarilytransmits information of the first PLMN on behalf of the first PLMNaccording to a pre-configured policy and operator command (e.g.,OAM-based command).

1) The UE receives the information of the first PLMN transmitted by thebase station of the second PLMN, and transmits an attach request messageto attempt access. The UE thinks it is access to the first PLMN, butactually transmits an attach request message to the MME of the secondPLMN via the base station of the second PLMN.

2) The MME of the second PLMN evaluates whether disaster roaming ispresent. The MME of the second PLMN performs interaction with the HSS ofthe third PLMN, which is the HPLMN of the UE, in order to check thesubscriber information of the UE, and checks the configured orpre-configured operator policies and roaming policies, etc. Ifnecessary, interaction with other network nodes, such as PCRF, may beperformed to check operator policies.

Through this process, it is determined whether to accept the access forproviding the disaster roaming service of the UE requesting access andthe range of the disaster roaming service that can be provided (e.g., abasic voice call and a specific service, etc.).

Case A: A case in which the affiliate policy allows service to beprovided through non-disaster operator

The roaming agreement between the first PLMN and the third PLMN mayinclude, in the event of a communication disaster in addition to thebasic roaming service, allowing some or all services such as voice callsto be provided via some network nodes of another operator network (e.g.,the second PLMN).

3A) The MME of the second PLMN processes the access request (i.e.,attach request) of the UE, which is a subscriber of the third PLMN, asin the case where the subscriber of the first PLMN requests access, andperforms a procedure for establishing a PDN connection for serviceprovision.

That is, the MME of the second PLMN performs an LBO or HR procedureaccording to the APN and operator policy to establish a PDN connectionfor the UE based on the roaming service providing technology.

3A-1) When the roaming service is provided by the LBO scheme, the MME ofthe second PLMN exchanges a create session request/response message withthe P-GW of the first PLMN, which is the local PLMN.

3A-2) When the roaming service is provided by the HR scheme, the MME ofthe second PLMN exchanges create session request/response messages withthe P-GW of the third PLMN, which is the HPLMN of the UE.

4A) After successfully establishing the PDN connection, the MME of thesecond PLMN transmits an attach accept message to the UE. In this case,information on disaster roaming may be explicitly or implicitlyincluded.

For reference, based on the information, the UE may indicate informationon the disaster roaming to the user (e.g., indication on the displayunit).

5A) IMS signaling is transmitted to an IMS network (e.g., P-CSCF)through the established PDN connection, and a voice service may beprovided to the UE.

5A-1) When the roaming service is provided by the LBO scheme, IMSsignaling is transmitted to the IMS network of the first PLMN via theS-GW of the second PLMN and the P-GW of the first PLMN, which is theLocal PLMN.

5A-2) When the roaming service is provided by the HR scheme, IMSsignaling is transmitted to the IMS network of the third PLMN throughthe S-GW of the second PLMN and the P-GW of the third PLMN, which is theHPLMN.

Case B: When the affiliate policy does not allow services to be providedthrough non-disaster operators, roaming services may not be provided tocope with disasters.

3B) In the disaster roaming evaluation of step 2, upon checking theroaming agreement, it was decided not to accept disaster roaming The MMEof the second PLMN transmits an attach reject message to the UE. In thiscase, information on disaster roaming may be explicitly or implicitlyincluded.

4B) Upon receiving the attach reject message, the UE evaluates thereason for rejection of the message and then performs PLMN re-selection.The UE manages the priority of the PLMN based on the disaster roaminginformation received in step 3. For example, in the case of a PLMN inwhich disaster roaming has occurred, control such as temporarily/for aspecific period of time lowering priority is included.

5B) The UE transmits an attach request message to the newly selectedPLMN. In this embodiment, it is assumed and described that the newlyselected PLMN is the second PLMN.

6B) The MME of the second PLMN performs a procedure for establishing aPDN connection.

7B) After the PDN connection is successfully established, the MME of thesecond PLMN transmits an attach accept message to the UE.

8B) IMS signaling is transmitted to an IMS network (e.g., P-CSCF)through the established PDN connection, and a voice service may beprovided. In this embodiment, IMS signaling is transmitted to the IMSnetwork of the second PLMN via the S-GW and the P-GW of the second PLMN.

FIG. 23a and FIG. 23b show an embodiment in which the disclosure of thepresent specification is applied to 5GS.

In FIG. 23a and FIG. 23 b, it is assumed that there is a roamingagreement between the first PLMN and the third PLMN, and a subscriber ofthe third PLMN can access the first PLMN to receive a roaming service.

In addition, in FIG. 23a and FIG. 23 b, it is assumed that acommunication service is impossible due to a communication disaster inthe first PLMN, and the base station of the second PLMN temporarilytransmits information of the first PLMN on behalf of the first PLMNaccording to a pre-configured policy and operator command (e.g.,OAM-based command)

1) The UE receives the information of the first PLMN transmitted by thebase station of the second PLMN, and transmits a registration requestmessage to attempt access. The UE thinks it is access to the first PLMN,but actually transmits a registration request message to the AMF of thesecond PLMN via the base station of the second PLMN.

2) The AMF of the second PLMN evaluates whether disaster roaming ispresent. The AMF of the second PLMN performs interaction with the UDM ofthe third PLMN, which is the HPLMN of the UE, in order to check thesubscriber information of the UE, and checks the configured orpre-configured operator policies and roaming policies, etc. Ifnecessary, interaction with other network nodes, such as PCF, may beperformed to check operator policies.

Through this process, it is determined whether to accept the access forproviding the disaster roaming service of the UE requesting access andthe range of the disaster roaming service that can be provided (e.g., abasic voice call and a specific service, etc.).

Case A: A case in which the affiliate policy allows service to beprovided through non-disaster operator

The roaming agreement between the first PLMN and the third PLMN mayinclude, in the event of a communication disaster in addition to thebasic roaming service, allowing some or all services such as voice callsto be provided via some network nodes of another operator network (e.g.,the second PLMN).

3A) The AMF of the second PLMN processes the registration requestmessage of the UE, which is a subscriber of the third PLMN, as in thecase where the subscriber of the first PLMN requests access, andtransmits a registration accept message. In this case, information ondisaster roaming may be explicitly or implicitly included.

For reference, based on the information, the UE may indicate informationon the disaster roaming to the user (e.g., indication on the displayunit).

4A) The UE transmits the PDU session establishment request message tothe SMF via the AMF. Based on the roaming service providing technology,the LBO or HR procedure is performed according to the DNN and operatorpolicy for establishing the PDU session requested by the UE.

Here, the difference from the examples of FIG. 22a and FIG. 22b is thatthe SMF may perform disaster roaming evaluation. That is, since the SMFcan allow a service only for a specific session, the range of theservice can be determined in this step.

4A-1) When roaming service is provided by the LBO scheme, the AMF of thesecond PLMN communicates with the SMF of the second PLMN, and the SMF ofthe second PLMN transmits/receives messages to communicate with the SMFof the first PLMN, which is the local PLMN. In this case, the SMF of thesecond PLMN serves as an Intermediate SMF (I-SMF). Alternatively,according to a deployment option for disaster roaming, the AMF of thesecond PLMN transmits/receives messages for direct communication withthe SMF of the first PLMN, which is a local PLMN.

4A-2) When roaming service is provided by the HR scheme, the AMF of thesecond PLMN communicates with the SMF of the second PLMN, and the SMF ofthe first PLMN transmits/receives messages to communicate with the SMFof the third PLMN, which is the HPLMN of the UE. In this case, the SMFof the second PLMN serves as a Visited SMF (V-SMF). Alternatively,according to a deployment option for disaster roaming, the AMF of thesecond PLMN transmits/receives messages for direct communication withthe SMF of the third PLMN, which is the HPLMN of the UE.

5A) IMS signaling is transmitted to an IMS network (e.g., P-CSCF)through the established PDU session, and a voice service may be providedto the UE.

5A-1) When the roaming service is provided by the LBO scheme, IMSsignaling is transmitted to the IMS network of the first PLMN via theUPF of the second PLMN and the UPF of the first PLMN, which is the localPLMN.

5A-2) When the roaming service is provided by the HR scheme, IMSsignaling is transmitted to the IMS network of the third PLMN throughthe UPF of the second PLMN and the UPF of the third PLMN, which is theHPLMN.

Case B: When the affiliate policy does not allow services to be providedthrough non-disaster operators, roaming services may not be provided tocope with disasters.

3B) In the disaster roaming evaluation of step 2, upon checking theroaming agreement, it was decided not to accept disaster roaming The AMFof the second PLMN transmits a registration reject message to the UE. Inthis case, information on disaster roaming may be explicitly orimplicitly included.

4B) Upon receiving the registration reject message, the UE evaluates thereason for rejection of the message and then performs PLMN re-selection.The UE manages the priority of the PLMN based on the disaster roaminginformation received in step 3. For example, in the case of a PLMN inwhich disaster roaming has occurred, control such as temporarily/for aspecific period of time lowering priority is included.

5B) The UE transmits a registration request message to the newlyselected PLMN. In this embodiment, it is assumed and described that thenewly selected PLMN is the second PLMN.

6B) After the registration is successfully performed, the UE performs aprocedure for establishing a PDU session.

7B) IMS signaling is transmitted to an IMS network (e.g., P-CSCF)through the established PDU session, and a voice service may beprovided. In this embodiment, IMS signaling is transmitted to the IMSnetwork of the second PLMN via the UPF of the second PLMN.

<Summary of the Disclosure of the Present Specification>

A disclosure of the present specification provides a method of accessinganother Public Land Mobile Network (PLMN) instead of a subscribed thirdPLMN. According to the method, the UE may access a second PLMN providinga service on behalf of a first PLMN which has a roaming agreement withthe third PLMN. And according to the method, the UE may displayinformation indicating access to the second PLMN on a screen. The secondPLMN may provide only a limited service.

The displayed information may be an icon or an indicator on a status bardisplayed on the screen of the UE.

The displayed information may be a signal strength from a base stationof the second PLMN.

The displaying of the information may comprise displaying that a signalstrength from a base station of the first PLMN is lowest instead ofdisplaying a signal strength from a base station of the second PLMN.

The displayed information may be a message indicating that the firstPLMN is not serviceable so the second PLMN has been accessed.

The message may include a list of limited services provided by thesecond PLMN.

The method may further comprise displaying icons of applications usingservices not provided by the second PLMN differently from other icons.

The method may further comprise displaying icons of applications usingservices not provided by the second PLMN in shade, black and white, ortransparently.

The method may further comprise displaying only icons of applicationsusing services provided by the second PLMN.

The services provided by the second PLMN may include at least one of acall service, a message service, and a limited data service.

A disclosure of the present specification provides a UE accessinganother Public Land Mobile Network (PLMN) instead of a subscribed thirdPLMN. The UE may include a transceiver configured to access a secondPLMN providing a service on behalf of a first PLMN which has a roamingagreement with the third PLMN. The UE may include a display unitconfigured to display information indicating access to the second PLMNon a screen of the UE. The second PLMN may provide only a limitedservice.

<Scenarios to which the Disclosure of the Present Specification isApplicable>

Hereinafter, scenarios to which the present disclosure is applicable aredescribed.

FIG. 24 illustrates a wireless communication system according to anembodiment.

Referring to FIG. 24, the wireless communication system may include afirst device 100 a and a second device 100 b.

The first device 100 a may be a base station, a network node, atransmission terminal, a reception terminal, a wireless device, awireless communication device, a vehicle, a vehicle on which aself-driving function is mounted, a connected car, a drone (UnmannedAerial Vehicle (UAV)), an Artificial Intelligence (AI) module, a robot,an Augmented Reality (AR) device, a Virtual Reality (VR) device, a MixedReality (MR) device, a hologram device, a public safety device, an MTCdevice, an Internet-of-Things (IoT) device, a medical device, a FinTechdevice (or financial device), a security device, a climate/environmentdevice, a device related to 5G service or a device related to the fourthindustrial revolution field.

The second device 100 b may be a base station, a network node, atransmission terminal, a reception terminal, a wireless device, awireless communication device, a vehicle, a vehicle on which aself-driving function is mounted, a connected car, a drone (UnmannedAerial Vehicle (UAV)), an Artificial Intelligence (AI) module, a robot,an Augmented Reality (AR) device, a Virtual Reality (VR) device, a MixedReality (MR) device, a hologram device, a public safety device, an MTCdevice, an Internet-of-Things (IoT) device, a medical device, a FinTechdevice (or financial device), a security device, a climate/environmentdevice, a device related to 5G service or a device related to the fourthindustrial revolution field.

For example, the UE may include a cellular phone, a smart phone, alaptop computer, a terminal for digital broadcasting, a Personal DigitalAssistants (PDA), a Portable Multimedia Player (PMP), a navigation, aslate PC, a tablet PC, an ultrabook, a wearable device (e.g., a watchtype terminal (smartwatch), a glass type terminal (smart glass), a HeadMounted Display (HMD)), and so on. For example, the HMD may be a displaydevice of a form, which is worn on the head. For example, the HMD may beused to implement VR, AR or MR.

For example, the drone may be a flight vehicle that flies by a wirelesscontrol signal without a person being on the flight vehicle. Forexample, the VR device may include a device implementing the object orbackground of a virtual world. For example, the AR device may include adevice implementing the object or background of a virtual world byconnecting it to the object or background of the real world. Forexample, the MR device may include a device implementing the object orbackground of a virtual world by merging it with the object orbackground of the real world. For example, the hologram device mayinclude a device implementing a 360-degree stereographic image byrecording and playing back stereographic information using theinterference phenomenon of a light beam generated when two lasers calledholography are met. For example, the public safety device may include avideo relay device or an imaging device capable of being worn on auser's body. For example, the MTC device and the IoT device may be adevice that does not require a person's direct intervention ormanipulation. For example, the MTC device and the IoT device may includea smart meter, a vending machine, a thermometer, a smart bulb, a doorlock or a variety of sensors. For example, the medical device may be adevice used for the purpose of diagnosing, treating, reducing, handlingor preventing a disease. For example, the medical device may be a deviceused for the purpose of diagnosing, treating, reducing or correcting aninjury or obstacle. For example, the medical device may be a device usedfor the purpose of testing, substituting or modifying a structure orfunction. For example, the medical device may be a device used for thepurpose of controlling pregnancy. For example, the medical device mayinclude a device for medical treatment, a device for operation, a devicefor (external) diagnosis, a hearing aid or a device for a surgicalprocedure. For example, the security device may be a device installed toprevent a possible danger and to maintain safety. For example, thesecurity device may be a camera, CCTV, a recorder or a blackbox. Forexample, the FinTech device may be a device capable of providingfinancial services, such as mobile payment. For example, the FinTechdevice may include a payment device or point of sales (POS). Forexample, the climate/environment device may include a device formonitoring or predicting the climate/environment.

The first device 100 a may include at least one processor such as aprocessor 1020 a, at least one memory such as memory 1010 a, and atleast one transceiver such as a transceiver 1031 a. The processor 1020 amay perform the above-described functions, procedures, and/or methods.The processor 1020 a may perform one or more protocols. For example, theprocessor 1020 a may perform one or more layers of a radio interfaceprotocol. The memory 1010 a is connected to the processor 1020 a, andmay store various forms of information and/or instructions. Thetransceiver 1031 a is connected to the processor 1020 a, and may becontrolled to transmit and receive radio signals.

The second device 100 b may include at least one processor such as aprocessor 1020 b, at least one memory device such as memory 1010 b, andat least one transceiver such as a transceiver 1031 b. The processor1020 b may perform the above-described functions, procedures and/ormethods. The processor 1020 b may implement one or more protocols. Forexample, the processor 1020 b may implement one or more layers of aradio interface protocol. The memory 1010 b is connected to theprocessor 1020 b, and may store various forms of information and/orinstructions. The transceiver 1031 b is connected to the processor 1020b and may be controlled transmit and receive radio signals.

The memory 1010 a and/or the memory 1010 b may be connected inside oroutside the processor 1020 a and/or the processor 1020 b, respectively,and may be connected to another processor through various technologies,such as a wired or wireless connection.

The first device 100 a and/or the second device 100 b may have one ormore antennas. For example, an antenna 1036 a and/or an antenna 1036 bmay be configured to transmit and receive radio signals.

FIG. 25 illustrates an example of 5G use scenarios.

The 5G usage scenarios illustrated in FIG. 25 are merely exemplary, andthe technical features of the present specification may also be appliedto other 5G usage scenarios that are not illustrated in FIG. 25.

Referring to FIG. 25, three major requirement areas of 5G include: (1)an enhanced Mobile Broadband (eMBB) area, (2) a massive Machine TypeCommunication (mMTC) area, and (3) an Ultra-Reliable and Low LatencyCommunications (URLLC) area. Some examples of usage may require multipleareas for optimization, while other examples of usage may focus only onone Key Performance Indicator (KPI). The 5G supports these variousexamples of usage in a flexible and reliable way.

The eMBB focuses generally on improvements in data rate, latency, userdensity, and capacity and coverage of mobile broadband access. The eMBBaims at a throughput of about 10 Gbps. The eMBB makes it possible to farsurpass basic mobile Internet access, and covers full-duplex operations,media in cloud or augmented reality, and entertainment applications.Data is one of the key drivers of 5G, and it may not be possible to seededicated voice services for the first time in the 5G era. In 5G, voiceis expected to be processed as an application program simply using dataconnection provided by a communication system. A main reason for anincreased traffic volume is an increase in content size and an increasein the number of applications requiring high data rates. Streamingservices (audio and video), interactive video and mobile Internetconnections will become more prevalent as more devices are connected tothe Internet. Many of these applications require always-on connectivityto push real-time information and notifications to users. Cloud storageand applications are rapidly increasing in mobile communicationplatforms, which may be applied to both work and entertainment. Cloudstorage is a special use case that drives the growth of uplink datarates. 5G is also used for remote work in the cloud and requires muchlower end-to-end latency to maintain a good user experience when tactileinterfaces are used. In entertainment, for example, cloud gaming andvideo streaming are another key factor requiring improvement in mobilebroadband capabilities. Entertainment is essential on smartphones andtablets anywhere, including in highly mobile environments such astrains, cars and airplanes. Another use case is augmented reality andinformation retrieval for entertainment. Here, augmented realityrequires very low latency and an instantaneous data amount.

The mMTC, which is designed to enable communication between a largenumber of low-cost devices powered by batteries, is provided to supportsmart metering, logistics, fields, and applications such as bodysensors. The mMTC aims at about 10-year batteries and/or about onemillion devices per km². The mMTC enables seamless connection ofembedded sensors in all fields to form a sensor network and is one ofthe most anticipated 5G use cases. Potentially, IoT devices arepredicted to reach 20.4 billion by 2020. Smart networks utilizingindustrial IoT is one of the areas where 5G plays a key role in enablingsmart cities, asset tracking, smart utilities, agriculture and securityinfrastructure.

The URLLC, which enables devices and machines to communicate with highreliability, very low latency, and high availability, are ideal forvehicle communications, industrial control, factory automation,telesurgery, smart grid, and public safety applications. The URLLC aimsat a delay of about 1 ms. The URLLC includes new services that willchange the industry through ultra-reliable/low-latency links such asremote control of key infrastructures and autonomous vehicles. Levels ofreliability and latency are essential for smart grid control, industrialautomation, robotics, and drone control and adjustment.

Next, a plurality of usage examples included in the triangle of FIG. 25will be described in more detail.

5G, which is a means of providing streams that are rated as hundreds ofmegabits per second to a gigabit per second, may complementFiber-To-The-Home (FTTH) and cable-based broadband (or Data Over CableService Interface Specifications (DOCSIS)). Such a high speed may berequired to deliver TVs with resolution of 4K or higher (6K, 8K andhigher) as well as Virtual Reality (VR) and Augmented Reality (AR). VRand AR applications involve almost immersive sports events. Specificapplications may require special network configuration. For example, inthe case of VR games, a game company may need to integrate a core serverwith an edge network server of a network operator to minimize latency.

Automotive is expected to be an important new driver for 5G togetherwith many use cases for mobile communication regarding vehicles. Forexample, entertainment for passengers require both high capacity andhigh mobile broadband. The reason is because future users will continueto expect high-quality connections, regardless of their location andspeed. Another use case in the automotive sector is an augmented realitydashboard. The augmented reality dashboard allows drivers to identifyobjects in the dark on top of what they see through a front window. Theaugmented reality dashboard superimposes information to be provided tothe driver regarding a distance and movement of objects. In the future,wireless modules will enable communication between vehicles, exchange ofinformation between a vehicle and a supporting infrastructure, andexchange of information between a vehicle and other connected devices(e.g., devices carried by pedestrians). A safety system may lower therisk of accidents by guiding the driver to alternative courses of actionto make driving safer. A next step will be a remotely controlled vehicleor an autonomous vehicle. This requires very reliable and very fastcommunication between different autonomous vehicles and/or betweenvehicles and infrastructure. In the future, autonomous vehicles willperform all driving activities and drivers will be forced to focus onlyon traffic anomalies that the vehicle itself cannot identify. Thetechnical requirements of autonomous vehicles require ultra-low latencyand ultra-fast reliability to increase traffic safety to levels thatcannot be achieved by humans.

Smart cities and smart homes referred to as smart society will beembedded with high-density wireless sensor networks as an example ofsmart networks. A distributed network of intelligent sensors willidentify the conditions for cost and energy efficient maintenance of acity or home. A similar setup may be done for each household.Temperature sensors, window and heating controllers, burglar alarms, andhome appliances are all wirelessly connected. Many of these sensorstypically require low data rates, low power, and low cost. However, forexample, real-time HD video may be required in certain types of devicesfor surveillance.

The consumption and distribution of energy including heat or gas ishighly decentralized, requiring automated control of distributed sensornetworks. A smart grid interconnects these sensors using digitalinformation and communication technologies to collect information andact accordingly. This information may include the behavior of suppliersand consumers, so that the smart grid may improve efficiency,reliability, economical efficiency, sustainability of production, and adistribution of fuels such as electricity in an automated manner. Thesmart grid may also be considered as another low-latency sensor network.

A health sector has many applications that may benefit from mobilecommunications. The communication system may support telemedicineproviding clinical care from remote locations. This may help reducebarriers to distance and improve access to medical services that are notconsistently available in remote rural areas. It is also used to savelives in critical care and emergencies. A wireless sensor network basedon mobile communication may provide remote monitoring and sensors forparameters such as a heart rate and blood pressure.

Wireless and mobile communications are becoming increasingly importantin industrial applications. Wiring is expensive to install and maintain.Thus, a possibility of replacing cables with reconfigurable wirelesslinks is an attractive opportunity for many industries. However,achieving this requires that a wireless connection operates with adelay, reliability and capacity similar to those of a cable and requiressimplified management. Low latency and very low error probability arenew requirements that need to be connected to 5G.

Logistics and cargo tracking is an important use case for mobilecommunications that enables tracking of inventory and packages fromanywhere using a location-based information system. Logistics andfreight tracking use cases typically require low data rates but requirea wide range and reliable location information.

<Artificial Intelligence (AI)>

Artificial intelligence refers to a field of studying artificialintelligence or a methodology for creating the same, and machinelearning refers to a field of defining various problems dealing in anartificial intelligence field and studying methodologies for solving thesame. The machine learning may be defined as an algorithm for improvingperformance with respect to a certain task through repeated experienceswith respect to the task.

An Artificial Neural Network (ANN) is a model used in machine learning.It can mean a whole model of problem-solving ability, consisting ofartificial neurons (nodes) that form a network of synapses. An ANN canbe defined by a connection pattern between neurons in different layers,a learning process for updating model parameters, and/or an activationfunction for generating an output value.

The ANN may include an input layer, an output layer, and optionally oneor more hidden layers. Each layer includes one or more neurons, and theANN may include neurons and synapses connecting neurons. In the ANN,each neuron may output a function value of an activation function forinput signals input through a synapse, a weight, and a bias.

A model parameter means a parameter determined through learning, andincludes the weight of the synaptic connection and the bias of theneuron. In addition, the hyperparameter refers to a parameter thatshould be set before learning in a machine learning algorithm, andincludes a learning rate, the number of iterations, a mini-batch size,an initialization function, etc.

The purpose of learning the ANN can be seen as determining the modelparameters that minimize the loss function. The loss function may beused as an index for determining optimal model parameters in thelearning process of the ANN.

Machine learning can be classified into supervised learning,unsupervised learning, and reinforcement learning according to alearning method.

Supervised learning may refer to a method of training the ANN in a statewhere a label for training data. The label may refer a correct answer(or result value) that the ANN should infer when training data is inputto the ANN. Unsupervised learning may refer to a method of training theANN in a state where no labels are given for training data.Reinforcement learning may refer to a learning method in which an agentdefined in a certain environment learns to select an action or sequenceof actions that maximizes the cumulative reward in each state.

Among ANNs, machine learning implemented as a Deep Neural Network (DNN)including a plurality of hidden layers is also called deep learning, anddeep learning is a part of machine learning. Hereinafter, machinelearning is used in a sense including deep learning.

<Robot>

A robot may refer to a machine which automatically handles a given taskby its own ability, or which operates autonomously. Particularly, arobot that functions to recognize an environment and perform anoperation according to its own judgment may be referred to as anintelligent robot.

Robots may be classified into, for example, industrial, medical,household, and military robots, according to the purpose or field ofuse.

A robot may include an actuator or a driving unit including a motor inorder to perform various physical operations, such as moving joints ofthe robot. In addition, a movable robot may include, for example, awheel, a brake, and a propeller in the driving unit thereof, and throughthe driving unit, may thus be capable of traveling on the ground orflying in the air.

<Self-Driving or Autonomous-Driving>

Autonomous driving refers to self-driving technology, and an autonomousvehicle refers to a vehicle that moves without any manipulation by auser or with minimum manipulation by a user.

For example, autonomous driving may include all of a technology forkeeping a vehicle within a driving lane, a technology for automaticallycontrolling a speed such as an adaptive cruise control, a technology forautomatically driving the vehicle along a determined route, and atechnology for, when a destination is set, automatically setting a routeand driving the vehicle along the route.

A vehicle includes a vehicle having only an internal combustion engine,a hybrid vehicle having both an internal combustion engine and anelectric motor, and an electric vehicle having only an electric motor,and may include not only an automobile but also a train, a motorcycle,or the like.

In this case, an autonomous vehicle may be considered as a robot with anautonomous driving function.

<Extended Reality; XR>

Extended reality collectively refers to Virtual Reality (VR), AugmentedReality (AR), and Mixed Reality (MR). The VR technology provides realworld objects or backgrounds only in CG images, the AR technologyprovides virtual CG images together with real object images, and the MRtechnology is computer graphic technology for mixing and combiningvirtual objects with the real world.

The MR technology is similar to the AR technology in that both real andvirtual objects are shown together. However, there is a difference inthat a virtual object is used to complement a real object in the ARtechnology, whereas a virtual object and a real object are used in anequivalent nature in the MR technology.

The XR technology may be applied to a Head-Mount Display (HMD), aHead-Up Display (HUD), a mobile phone, a tablet PC, a laptop, a desktop,a TV, digital signage, etc. A device to which the XR technology isapplied may be referred to as an XR device.

FIG. 26 shows an AI system 1 according to an embodiment.

Referring to FIG. 26, an AI system 1 is connected to at least one of anAI server 200, a robot 100 a, a self-driving vehicle 100 b, an XR device100 c, a smartphone 100 d, or home appliances 100 e over a cloud network10. In this case, the robot 100 a, the self-driving vehicle 100 b, theXR device 100 c, the smartphone 100 d or the home appliances 100 e towhich the AI technology has been applied may be called AI devices 100 ato 100 e.

The cloud network 10 may be a network that constitutes a part of a cloudcomputing infrastructure or a network that exists in the cloud computinginfrastructure. Here, the cloud network 10 may be configured using a 3Gnetwork, a 4G or LTE network, or a 5G network.

The devices 100 a to 100 e and 200 configuring the AI system 1 may beinterconnected over the cloud network. Particularly, the devices 100 ato 100 e and 200 may communicate with each other through a base stationbut may directly communicate with each other without the intervention ofa base station.

The AI server 200 may include a server that performs AI processing and aserver that performs an operation on big data.

The AI server 200 is connected to at least one of the robot 100 a, theself-driving vehicle 100 b, the XR device 100 c, the smartphone 100 d orthe home appliances 100 e, that is, AI devices configuring the AIsystem, over the cloud network 10 and may help at least some of the AIprocessing of the connected AI devices 100 a to 100 e.

In this case, the AI server 200 may train an artificial neural networkbased on a machine learning algorithm in place of the AI devices 100 ato 100 e, may directly store a learning model or may transmit thelearning model to the AI devices 100 a to 100 e.

In this case, the AI server 200 may receive input data from the AIdevices 100 a to 100 e, may deduce a result value of the received inputdata using the learning model, may generate a response or controlcommand based on the deduced result value, and may transmit the responseor control command to the AI devices 100 a to 100 e.

Alternatively, the AI devices 100 a to 100 e may directly deduce aresult value of input data using a learning model and may generate aresponse or control command based on the deduced result value.

Hereinafter, various embodiments of the AI devices 100 a to 100 e towhich the aforementioned technology is applied will be described.

<AI+Robot>

The robot 100 a, which adopts an AI technology, may be implemented as aguide robot, a transport robot, a cleaning robot, a wearable robot, anentertainment robot, a pet robot, an unmanned flying robot, and thelike.

The robot 100 a may include a robot control module for controlling anoperation, and the robot control module may refer to a software moduleor a chip implemented with hardware.

The robot 100 a may acquire status information of the robot 100 a usingsensor information acquired from various types of sensors, detect(recognize) surrounding environments and objects, generate map data,determine moving routes and driving plans, determine responses to userinteractions, or determine actions.

Here, the robot 100 a may use sensor information obtained from at leastone sensor from among LIDAR, radar, and camera to determine a movingroute and a driving plan.

The robot 100 a may perform the above operations using a learning modelincluding at least one artificial neural network. For example, the robot100 a may recognize a surrounding environment and an object using alearning model and may determine an operation using the recognizedsurrounding environment information or object information. Here, thelearning model may be directly learned by the robot 100 a or learned byan external device such as the AI server 200.

Here, the robot 100 a may directly generate a result using a learningmodel and perform an operation, or transmit sensor information to anexternal device such as the AI server 200, receive a result generatedaccordingly, and perform an operation.

The robot 100 a may determine a moving path and a driving plan using atleast one of map data, object information detected from sensorinformation, or object information acquired from an external device, andcontrol a driving unit to drive the robot 100 a according to the movingpath and the driving plan.

The map data may include object identification information on variousobjects arranged in a space in which the robot 100 a moves. For example,the map data may include object identification information on fixedobjects such as walls and doors and movable objects such as flower potsand desks. In addition, the object identification information mayinclude a name, a type, a distance, and a location.

In addition, the robot 100 a may perform an operation or run bycontrolling the driving unit based on the user's control/interaction. Inthis case, the robot 100 a may acquire interaction intention informationaccording to a user's motion or voice speech, determine a response basedon the acquired intention information, and perform an operation.

<AI+Autonomous-Driving/Self-Driving>

The autonomous vehicle 100 b may be implemented as a mobile robot, avehicle, an unmanned aerial vehicle, etc., to which AI technology isapplied.

The autonomous vehicle 100 b may include an autonomous driving controlmodule for controlling the autonomous driving function, and theautonomous driving control module may refer to a software module and/ora chip implementing the software module. The autonomous driving controlmodule may be included in the autonomous vehicle 100 b as a component ofthe autonomous vehicle 100 b, but may be connected to the outside of theautonomous vehicle 100 b with separate hardware.

The autonomous vehicle 100 b may acquire the state information of theautonomous vehicle 100 b using the sensor information acquired fromvarious kinds of sensors and/or detect (recognize) the surroundingenvironment and/or the object, and/or generate map data, and/ordetermine a travel route and/or a travel plan, and/or determine anoperation.

Like the robot 100 a, the autonomous vehicle 100 b can use the sensorinformation acquired from at least one sensor among the LIDAR, theradar, and/or the camera to determine the travel route and/or the travelplan.

In particular, the autonomous vehicle 100 b can recognize an environmentand/or an object for an area in which the field of view is obscuredand/or over a certain distance by receiving sensor information fromexternal devices, and/or receive the recognized information directlyfrom external devices.

The autonomous vehicle 100 b can perform the above-described operationsusing a learning model composed of at least one ANN. For example, theautonomous vehicle 100 b can recognize the surrounding environmentand/or the object using the learning model, and can determine the travelroute using the recognized surrounding information and/or the objectinformation. The learning model may be learned directly from theautonomous vehicle 100 b and/or learned from an external device such asthe AI server 200.

In this case, the autonomous vehicle 100 b may perform an operation bygenerating a result using a direct learning model, but the autonomousvehicle may also perform operation by transmitting sensor information toan external device such as the AI server 200 and receiving the generatedresult.

The autonomous vehicle 100 b may determine the travel route and/or thetravel plan using at least one of the map data, the object informationdetected from the sensor information and/or the object informationacquired from the external device, and drive the autonomous vehicle 100b according to the determined travel route and/or travel plan bycontrolling the driving unit.

The map data may include object identification information on variousobjects arranged in a space (e.g. road) in which the autonomous vehicle100 b moves. For example, the map data may include object identificationinformation on fixed objects such as street lamps, rocks, and buildings,and/or on movable objects such as vehicles and pedestrians. The objectidentification information may include a name, a type, a distance,and/or a position, etc.

Also, the autonomous vehicle 100 b may perform the operation and/or runby controlling the driving unit based on the control/interaction of theuser. The autonomous vehicle 100 b may acquire the intention informationof the interaction due to the user's operation and/or voice utterance,determine the response based on the acquired intention information, andperform the operation.

<AI+XR>

The XR device 100 c may be implemented as a HMD, a HUD, a TV, a mobilephone, a smartphone, a computer, a wearable device, a home appliance, adigital signage, a vehicle, a fixed robot, a mobile robot, etc., towhich AI technology is applied.

The XR device 100 c analyzes the three-dimensional point cloud dataand/or image data acquired from various sensors and/or from an externaldevice to generate position data and/or attribute data for thethree-dimensional points, thereby obtaining information about thesurrounding space and/or the real object, and outputting the rendered XRobject. For example, the XR device 100 c may output an XR object, whichincludes the additional information about the recognized object, bycorresponding to the recognized object.

The XR device 100 c can perform the above-described operations using alearning model composed of at least one ANN. For example, the XR device100 c can recognize a real object from three-dimensional point clouddata and/or image data using the learning model, and can provideinformation corresponding to the recognized real object. The learningmodel may be learned directly from the XR device 100 c and/or learnedfrom an external device such as the AI server 1200.

In this case, the XR device 100 c may perform an operation by generatinga result using a direct learning model, but the autonomous vehicle mayalso perform operation by transmitting sensor information to an externaldevice such as the AI server 200 and receiving the generated result.

<AI+Robot+Autonomous-Driving/Self-Driving>

The robot 100 a may be implemented as a guide robot, a carrying robot, acleaning robot, a wearable robot, an entertainment robot, a pet robot,an unmanned flying robot, etc., to which AI technology andautonomous-driving technology are applied.

The robot 100 a, to which the AI technology and the autonomous-drivingtechnology are applied, may mean the robot 100 a having theautonomous-driving function itself and/or the robot 100 a interactingwith the autonomous vehicle 100 b.

The robot 100 a having an autonomous-driving function can collectivelyrefer to devices that move by themselves in accordance with a giventravel route and/or move by determining the traveling route bythemselves without user's control.

The robot 100 a having the autonomous-driving function and theautonomous vehicle 100 b can use a common sensing method to determine atleast one of the travel route and/or the travel plan. For example, therobot 100 a having the autonomous-driving function and the autonomousvehicle 100 b can determine at least one of the travel route and/or thetravel plan using the information sensed through the LIDAR, the radar,and/or the camera.

The robot 100 a interacting with the autonomous vehicle 100 b may existseparately from the autonomous vehicle 100 b, and the robot 100 ainteracting with the autonomous vehicle 100 b may be associated with theautonomous-driving function inside and/or outside the autonomous vehicle100, and/or may perform an operation associated with the user aboard theautonomous vehicle 100 b.

The robot 100 a interacting with the autonomous vehicle 100 b mayacquire the sensor information on behalf of the autonomous vehicle 100 band provide it to the autonomous vehicle 100 b, or the robot 100 ainteracting with the autonomous vehicle 100 b may obtain the sensorinformation and generate the environment information and/or the objectinformation to provide the autonomous vehicle 100 b, thereby controllingand/or assisting the autonomous-driving function of the autonomousvehicle 100 b.

Or, the robot 100 a interacting with the autonomous vehicle 100 b maymonitor the user boarding the autonomous vehicle 100 b and/or maycontrol the functions of the autonomous vehicle 100 b throughinteraction with the user. For example, when it is determined that thedriver is in a drowsy state, the robot 100 a may activate theautonomous-driving function of the autonomous vehicle 100 b and/orassist the control of the driving unit of the autonomous vehicle 100 b.The function of the autonomous vehicle 100 b controlled by the robot 100a may include not only an autonomous-driving function but also afunction provided by a navigation system and/or an audio system providedin the autonomous vehicle 100 b.

Or, the robot 100 a interacting with the autonomous vehicle 100 b mayprovide information and/or assist the function to the autonomous vehicle100 b outside the autonomous vehicle 100 b. For example, the robot 100a, such as a smart traffic light, may provide traffic informationincluding signal information, etc., to the autonomous vehicle 100 b. Therobot 100 a, such as an automatic electric charger of an electricvehicle, may interact with the autonomous vehicle 100 b to connect theelectric charger to the charging hole automatically.

<AI+Robot+XR>

The robot 100 a may be implemented as a guide robot, a carrying robot, acleaning robot, a wearable robot, an entertainment robot, a pet robot,an unmanned flying robot, a drone, etc., to which AI technology and XRtechnology are applied.

The robot 100 a to which the XR technology is applied may refer to arobot that is subject to control/interaction in the XR image. In thiscase, the robot 100 a may be separated from the XR device 100 c and canbe associated with each other.

When the robot 100 a that is the subject to control/interaction in theXR image acquires the sensor information from the sensors including thecamera, the robot 100 a and/or the XR device 100 c may generate an XRimage based on the sensor information and the XR device 100 c can outputthe generated XR image. The robot 100 a can operate based on a controlsignal and/or a user's interaction input through the XR device 100 c.

For example, the user can acknowledge the XR image corresponding to theviewpoint of the robot 100 a remotely linked through the external devicesuch as the XR device 100 c, and can adjust the autonomous travel pathof the robot 100 a, control operation and/or driving, or check theinformation of neighboring objects, through interaction.

<AI+Autonomous-Driving/Self-Driving+XR>

The autonomous vehicle 100 b may be implemented as a mobile robot, avehicle, an unmanned aerial vehicle, etc., to which AI technology and XRtechnology are applied.

The autonomous driving vehicle 100 b to which the XR technology isapplied may mean an autonomous vehicle having means for providing an XRimage and/or an autonomous vehicle that is subject tocontrol/interaction in the XR image. Particularly, the autonomousvehicle 100 b that is subject to control/interaction in the XR image maybe separated from the XR device 100 c and can be associated with eachother.

The autonomous vehicle 100 b having the means for providing the XR imagecan acquire the sensor information from the sensors including the cameraand output the generated XR image based on the acquired sensorinformation. For example, the autonomous vehicle 100 b may include anHUD to output an XR image, thereby providing a passenger with a realobject and/or an XR object corresponding to an object in the screen.

At this time, when the XR object is output to the HUD, at least a partof the XR object may be output so as to overlap with the actual objectthat the passenger's gaze is directed to. On the other hand, when the XRobject is output to the display provided in the autonomous vehicle 100b, at least a part of the XR object may be output so as to overlap withthe object in the screen. For example, the autonomous vehicle 100 b canoutput XR objects corresponding to objects such as a lane, anothervehicle, a traffic light, a traffic sign, a two-wheeled vehicle, apedestrian, a building, etc.

When the autonomous vehicle 100 b that is the subject tocontrol/interaction in the XR image acquires the sensor information fromthe sensors including the camera, the autonomous vehicle 100 b and/orthe XR device 100 c may generate an XR image based on the sensorinformation and the XR device 100 c can output the generated XR image.The autonomous vehicle 100 b can operate based on a control signaland/or a user's interaction input through the XR device 100 c.

In the above, preferred embodiments have been exemplarily described, butthe disclosure of the present specification is not limited to suchspecific embodiments, and thus, it may be modified, changed, or improvedin various forms within the scope set forth in the claims.

What is claimed is:
 1. A method of accessing another Public Land MobileNetwork (PLMN) instead of a subscribed third PLMN, the methodcomprising: accessing a second PLMN providing a service on behalf of afirst PLMN which has a roaming agreement with the third PLMN; anddisplaying information indicating access to the second PLMN on a screenof a User Equipment (UE), wherein the second PLMN provides only alimited service.
 2. The method of claim 1, wherein the displayedinformation is an icon or an indicator on a status bar displayed on thescreen of the UE.
 3. The method of claim 1, wherein the displayedinformation is a signal strength from a base station of the second PLMN.4. The method of claim 1, wherein the displaying of the informationcomprises displaying that a signal strength from a base station of thefirst PLMN is lowest instead of displaying a signal strength from a basestation of the second PLMN.
 5. The method of claim 1, wherein thedisplayed information is a message indicating that the first PLMN is notserviceable so the second PLMN has been accessed.
 6. The method of claim5, wherein the message includes a list of limited services provided bythe second PLMN.
 7. The method of claim 1, wherein the method furthercomprises displaying icons of applications using services not providedby the second PLMN differently from other icons.
 8. The method of claim1, wherein the method further comprises displaying icons of applicationsusing services not provided by the second PLMN in shade, black andwhite, or transparently.
 9. The method of claim 1, wherein the methodfurther comprises displaying only icons of applications using servicesprovided by the second PLMN.
 10. The method of claim 9, wherein theservices provided by the second PLMN includes at least one of a callservice, a message service, and a limited data service.
 11. A UserEquipment (UE) accessing another Public Land Mobile Network (PLMN)instead of a subscribed third PLMN, the UE comprising: a transceiverconfigured to access a second PLMN providing a service on behalf of afirst PLMN which has a roaming agreement with the third PLMN; and adisplay unit configured to display information indicating access to thesecond PLMN on a screen of the UE, wherein the second PLMN provides onlya limited service.
 12. The UE of claim 11, wherein the displayedinformation is an icon or an indicator on a status bar displayed on thescreen of the UE.
 13. The UE of claim 11, wherein the displayedinformation is a signal strength from a base station of the second PLMN.14. The UE of claim 11, wherein the display unit is configured todisplay that a signal strength from a base station of the first PLMN islowest instead of displaying a signal strength from a base station ofthe second PLMN.
 15. The UE of claim 11, wherein the displayedinformation is a message indicating that the first PLMN is notserviceable so the second PLMN has been accessed.
 16. The UE of claim15, wherein the message includes a list of limited services provided bythe second PLMN.
 17. The UE of claim 11, wherein the display unit isconfigured to display icons of applications using services not providedby the second PLMN differently from other icons.
 18. The UE of claim 11,wherein the display unit is configured to display icons of applicationsusing services not provided by the second PLMN in shade, black andwhite, or transparently.
 19. The UE of claim 11, wherein the displayunit is configured to display only icons of applications using servicesprovided by the second PLMN.
 20. The UE of claim 19, wherein theservices provided by the second PLMN includes at least one of a callservice, a message service, and a limited data service.